Fourth way: Overkill - Calculate both numbers by hand

@pneumaniac14

3 жыл бұрын

Even more over kill, take the logarithm of both sides and use binets log gamma functions.

@anindyaprithvi3585

3 жыл бұрын

@@pneumaniac14 even more overkill, use logarithm and Fermat's approximation

@MudahnyaFizik

3 жыл бұрын

It's called the brute force

@shivansh668

3 жыл бұрын

I think it is 1st one i.e. simple As the Michael said

@wasitahmid749

3 жыл бұрын

Hyperkill subtract 50^99 FROM 99! In head and write the result in 10 secs

They are equal! I typed them both into my calculator, and they both evaluated to “overflow error”!

@lucassalomao4882

3 жыл бұрын

Kkkkkkkkkk

@Fierywell

3 жыл бұрын

@@lucassalomao4882 ok?

@lucassalomao4882

3 жыл бұрын

@@Fierywell ok o que??

@Fierywell

3 жыл бұрын

@@lucassalomao4882 oh spanish I see

@lucassalomao4882

3 жыл бұрын

A vc é gringo kk. Pelo nome "Pedro" achei q fosse BR irmao

I was expecting wolframalpha for the third method...

@MamuelMuel

3 жыл бұрын

"by inspection"

@GKinWor

3 жыл бұрын

isnt it

@anmoldeepsingh9281

3 жыл бұрын

Can you help me with number of digits in a factorial without a program... I really want to prove this by inequality of number of digits. Edit: Nevermind.. got it.. stumbled upon Stirling’s approximation

@paritosh4643

3 жыл бұрын

BPRP! Nice to see you here :)

@flutcubasahmet1303

3 жыл бұрын

😂

The way we know that all the pairings are greater than one is that the denominators (51×49, 52×48, ... ,99×1) are of the form (50+n)(50-n) = 50^2-n^2 < 50^2

@jesusthroughmary

3 жыл бұрын

This is what I did to know in 5 seconds

@jesusthroughmary

3 жыл бұрын

Still watching to see whether this is one of his three ways

@abderrahmanyousfi5565

3 жыл бұрын

👍🏻👍🏻

@takyc7883

3 жыл бұрын

That’s clever

@obst3085

3 жыл бұрын

Yeah, was very surprised to not see that by him, feels very intuitive

1:44 "Notice 49 + 49 is 98, plus one is ... 50" I learn something new everyday lol

@patryslawfrackowiak6690

3 жыл бұрын

yeah, that was great :D

@xevira

3 жыл бұрын

This must be that "new" math I've been hearing about.

@Scrub_Lord-en7cq

3 жыл бұрын

@@xevira it’s called h (t)= am

@TheNatureWatcher

3 жыл бұрын

I do that sometimes talking not about math

@jamirimaj6880

3 жыл бұрын

@@xevira alternative math lol

This is deeply related to 'e'. If you look at the power expansion of 'e', you'll find this form. It turns out the question of when the denominator starts to dominate the numerator is exactly a factor of 'e' away from the number. So, in this case, you'll see that 50 * e will be the place where the denominator starts to dominates the numerator. Now, floor of 50 * e = 135. So, (50^134) / (134!) is greater than 1, but (50^135) / (135!) will be less than 1. This then ties into the length of the side of the higher dimensional square, given an area of n!. So, 'e' is actually a constant that relates area and parameters between dimensions. As a consequence, you get the limit n / (n!)^(1/n) as n goes to infinity = e Try the limit out on wolfram alpha

@jedinxf7

2 жыл бұрын

awesome!

@hagenfarrell

Жыл бұрын

@DukeOfDystopiaeither self taught, or they are a math major at uni.

@JPuree

12 күн бұрын

When I plug this into wolframalpha, I get 50^134/(134!) < 1. The crossover point occurs between 132 and 133.

3rd way: super easy, barely an inconvenience

@tamarpeer261

3 жыл бұрын

Comments: you could have used amgm Whoops! Whoopsie!

@crko34

3 жыл бұрын

Using wolfram alpha is tight

@riseciv7991

3 жыл бұрын

wow wow wow wow

@leif1075

3 жыл бұрын

@@tamarpeer261 whsts that arithmetic versus geometric mean you mean?

@AbhishekKumar-uu4uj

3 жыл бұрын

I understand your reference

At 3:35, I think a great way to show that all of the denominators are smaller than the numerators is by using difference of squares. You can express every denominator as (50 - n)(50 + n) for 0 < n < 50. This is equivalent to 50^2 - n^2, which is always smaller than 50^2.

@simonkiesewetter7389

Жыл бұрын

I was looking for that.

after having watched the first part: its basically squares vs. rectangles. when you have a set length of all sides combined, the surface area is always biggest when you make it a square. the longer and slimmer it gets, the less area it has (down to a line with no surface)

@Flimzes

3 жыл бұрын

I was thinking the same thing, he just proved that for a given circumference, a square gives the largest area of any rectangle

@venky1777

3 жыл бұрын

Great observation

@martinsonnleitner5516

3 жыл бұрын

Thought exactly the same! Also way more elegant than the brute force induction! 👍👍

@paneerpulao

3 жыл бұрын

Yeah I like to say it in this way (x)(x) > (x-a)(x+a)

@sirnate9065

2 жыл бұрын

This was exactly my first thought as well! Although I would've explained it much less clearly.

Thanks for another great video! Though I think it would've been good to note that e.g. 49*51=(50-1)(50+1) , and 48*52=(50-2)(50+2) etc. so all of the denominators are of the form (50-a)(50+a) which is 50^2-a^2 so it's less than 50^2.

@divyanshaggarwal6243

3 жыл бұрын

I dont think it was necessary to make a rigorous proof of the statement.Though in an exam scenario, it would probably be necessary.

@wyseebbah7193

3 жыл бұрын

@@divyanshaggarwal6243 Yah, it definitely isn't necessary. It's much easier than calculating though as you don't even have to look at numbers. It's a bit harder to explain I would guess though.

@michawielgus9827

3 жыл бұрын

It actually is easier since you dont need to calculate 49*51 etc, just show that a^2

@plaplanet

Жыл бұрын

そうそう

10:08 That’s a silent way to stop

@ivanlazaro7444

3 жыл бұрын

Spanish troupe?

@javizaragoza1463

3 жыл бұрын

@@ivanlazaro7444 confirmamos

@elcalabozodelandroide2

3 жыл бұрын

@@ivanlazaro7444 confirmo

I like the ending... for some reasons :p

1:45 2:20 ...and that's a good place to check your arithmetic.

Take the 99th root of both sides and apply the AM-GM inequality.

@davidepierrat9072

3 жыл бұрын

yeah smh...

@Kokurorokuko

3 жыл бұрын

wow, nice method!

@user-wo5ug7sl9z

3 жыл бұрын

that was what I thought

@pandas896

3 жыл бұрын

There's one more

@pandas896

3 жыл бұрын

Method

Take logs on both sides, we have 99*log(50) > log(1) + ... + log(99) by Jensen's inequality since the logarithm is concave.

@TechToppers

3 жыл бұрын

Bruh... I'm weak at inequality...

@samba272

3 жыл бұрын

Jensen's inequality has a less or equal sign in it, not a less than sign.

@ahmedhamdy2870

3 жыл бұрын

Or take log base 99 equals !

@gamer966

3 жыл бұрын

That's what I first thought! Kudos!

@Merlin1908

3 жыл бұрын

While true, using Jensen here is definitely overkill. The general case follows directly from AM-GM by noting the arithmetic mean of 1,2,...,n is (n+1)/2, so (n+1)/2 is at least the geometric mean, which is the n’th root of n!. Take n’th powers, and we get the general case.

I'm sure we all figured this out as kids when we wondered which two numbers, that add up to the same sum, would make the biggest rectangle. the longer the rectangle becomes, the smaller the area, and a square is the most efficient rectangle in this way.

@enderallygolem

3 жыл бұрын

The longer the rectangle the smaller the area I know what you mean but L

I thought the third method was only called "cheating" as sort of an expression to say it's figured out by doing some dirty tricks, like making some sort of a guess we couldn't possibly know and then proving it, but no... It's literally cheating. I didn't see that coming!

@spacescopex

2 жыл бұрын

MY SOLUTIONS: kzread.info/dash/bejne/h66B27iRg5O-fco.html kzread.info/dash/bejne/dJyom7dumpqclrw.html

4th way. Apply the “engineer’s function” and make everything equal to 3.

@ianmoseley9910

3 жыл бұрын

3black1red Reminds me of the old comment about mathematicians want the exact answer, engineers are happy if the numbers are a reasonable match and astronomers are ecstatic if they have the roughly the same order of magnitude

@TS-jm7jm

3 жыл бұрын

@@ianmoseley9910 brilliant

@Pandajannick

3 жыл бұрын

oh yes, like that pie number

@neutronenstern.

3 жыл бұрын

yea pi=3=e pi^2=g (thats actually pretty damn close due to the old definition of a meter being the length of a pendulum with a period of two seconds. With this definition g would be exactly pi^2 m/s^2 and if you are confused now since g has to be the same even if the def of a meter isnt the same, then you are not completely right. because g is 38622 inch/s^2)

@hybmnzz2658

3 жыл бұрын

Haha great joke bro. Definitely could not see it coming in this math puzzle video specifically about comparing arithmetic values. Jokes are hilarious when they are as innovative as this!

A 4th way of doing it : the AM-GM inequality yields ((50+k+50-k)/2))^2=50^2>=(50+k)(50-k) so taking the product over the k's between 0 and 49 we get 50^100>=50*99! hence the result Edit : or (50+k)(50-k)=50^2-k^2

@joshuamason2227

3 жыл бұрын

Genius!

@think_logically_

3 жыл бұрын

This is effectively the first method, only you proved the inequality, while I didn't notice the proof in the video. I did in less fashionate way, Consider trinomial x²-99x+2500 Since D=99²-10000=99²-100²0 for any x. In particular, k(99-k) n! (second method), from ((n+1)/2+k)((n+1)/2-k) < ((n+1)/2)². I believe this is simpler than by induction.

@spacescopex

2 жыл бұрын

Better method: kzread.info/dash/bejne/fZ2e2Lh_cdieh6w.html （2 topics included）

We could use Stirling's approximation too. n! ~ sqrt(2*pi*n)*(n/e)^n If we cancel some terms at the end: (1/2)^n > (1/e)^n we could get a pretty good correlation between two general forms!

I went straight to thinking about area ... where we know the largest area (multiplication of the two sides) for a given circumference is when the sides are equal. So we know that n^2 > (n-k)*(n+k) for any k {1,n-1}

@anonymous_4276

3 жыл бұрын

Excellent! So you basically maximized the volume of a 99-dimensional cube given the sum of the lengths of it's sides is constant. I guess this can also be used to show the general case of ((n+1)/2)^n>n!

I guessed correctly from my experiences in carpentry and ordering materials. I thought it was interesting that perfectly square rooms only had a difference of 1 compared to rooms that had dimensions of the same square room +1 and -1 10 x 10 = 100 9 x 11 = 99 Extrapolating the method further, I learned it was the difference of squares. 10 x 10 example: From 100 9 x 11 = 99 difference of 1 squared 8 x 12 = 96 difference of 2 squared 7 x 13 = 91 difference of 3 squared 6 x 14 = 84 difference of 4 squared And so on. Math can strangely be fun especially showing the kids interesting tricks like this. Thank you.

@spacescopex

2 жыл бұрын

MY SOLUTIONS: kzread.info/dash/bejne/h66B27iRg5O-fco.html kzread.info/dash/bejne/dJyom7dumpqclrw.html

@Misteribel

2 жыл бұрын

Why does this remind me of the “99 bottles of beer” song? 😝

Thanks Michael for the Videos. Your clarity of explanation, and detail in the solutions is the best I’ve seen.

I paired the terms of each series the same way that Michael did (99*1, 98*2, ... 51*49), and noted that each product has the form (50+k)(50-k). That equals 50^2-k^2. However, the pairwise products in 50^99 are always 50*50, and 50^2 is obviously larger than 50^2 minus k^2.

Nice video, as always, but I think that in the simple solution, when you talked about the "denominators increasing but being less than 50^2", you could, instead, just say that those pairs in the denominator are of the form (50-k)(50+k)=50^2-k^2, which is less than 50^2 for every k between 1 and 49 (both included). This way you don't need to explain why the denominators are increasing or even calculate the values of 50^2 and 49x51.

@spacescopex

2 жыл бұрын

MY SOLUTIONS: kzread.info/dash/bejne/h66B27iRg5O-fco.html kzread.info/dash/bejne/dJyom7dumpqclrw.html

Another way to think about it is that (x+n)(x-n) is always smaller than x^2 for any integer 'n' that isn't 0. Basically, having 99 of the same number multiplied together must be larger than an equivalent number of different numbers multiplied together. If you did (50^97)×(51)(49), it would also be smaller than 50^99, for the same reason.

Great work Michael!!

I'm so glad I found your channel! Plz keep up the good work!

I think we can use also log function. 99!/50^99 = (99/50)(98/50)•••(2/50)(1/50) Use log function log(99/50) + log(98/50) + ••• + log(2/50) + log(1/50) log(1+(k/n)) (n>0, k>0)] So 50^99 > 99! (I'm korean so I can't good english speaking. sorry guys)

@aradhya9550

Жыл бұрын

How do you know -log(1-(k/n)) > log(1+(k/n)) (n>0, k>0)]

10:15 Don’t be too hard on yourself and don’t forget to stay hydrated. No homework today, sorry folks. If you want a particular topic for the next one, tell me.

@Guilherme-xp1tv

3 жыл бұрын

Is this the first non spoken "good place to stop"?

@goodplacetostop2973

3 жыл бұрын

@@Guilherme-xp1tv I think it is

@adeolugboji3645

3 жыл бұрын

Can you do a counting/combinatorics question please?

@stephenbeck7222

3 жыл бұрын

Guilherme Castro Dela Corte, we need to get his kid to stroll up to the chalkboard and hold up a “that’s a good place to stop” poster.

@elihowitt4107

3 жыл бұрын

Something w inveriants

Thanks for another great video!

I really enjoyed working through this with the video

Thanks PROF. I LOVE YOUR TEACHING AND BECAUSE OF YOU I'M LOVING OLYMPIAD MATH GOOD JOB KEEP IT UP ! 💯K

@spacescopex

2 жыл бұрын

MY SOLUTIONS: kzread.info/dash/bejne/h66B27iRg5O-fco.html kzread.info/dash/bejne/dJyom7dumpqclrw.html

One of the best ending ever on this channel , I loved it 🤩❤️

@spacescopex

2 жыл бұрын

MY SOLUTIONS: kzread.info/dash/bejne/h66B27iRg5O-fco.html kzread.info/dash/bejne/dJyom7dumpqclrw.html

For the second method you can just used AM-GM and sub in 1, 2, 3…n and it comes out straight away

Thank you, Mr. Penn, very cool!

The "cheating way" was the best, I laughed a lot

@spacescopex

2 жыл бұрын

MY SOLUTIONS: kzread.info/dash/bejne/h66B27iRg5O-fco.html kzread.info/dash/bejne/dJyom7dumpqclrw.html

4th way : MULTIPLY BOTH SIDE BY ZEROES. And Tadaaaa You Get Equality.

@justanub4697

3 жыл бұрын

It doesn't work like that tho I mean it's a good joke, maybe

Fun problem! The first thing I thought of was to use the concavity of log. Which is very simple and also implies the AM-GM inequality and proves a pretty general version of this result.

You always work the devine problems of Math with clear and calm solution. I really need helps from teacher like you. Noone of my teachers have ever taught me as how you teach here. Warm regard from Indonesia.

Pre-watch guess: 50^99 Reasoning: both have 99 terms. I know that usually the central term multiplied with itself is bigger than outside numbers multiplied with each other. We'll see if it holds up.

@luislaracuente

Жыл бұрын

That was my logic too.

I initially thought this was an overkill video. Missing your overkill vids.

Hey, I really enjoy and like your video's! I was just looking on the internet what you do and found your website and I really loved your statement there "giving introverted student the opportunity to speak up and contribute.."! I never had such a teacher but I think that's a very important pro every teacher should have!

@maharanirani54

3 жыл бұрын

What is the website?

Thanks for the video sir! 👍🏻

1:44 "Notice 49 + 49 is 98, plus one is 50" Too many 50s to keep track of, I suspect

@david_ga8490

3 жыл бұрын

XD

@merlinrainbow2804

3 жыл бұрын

I felt like I was so good at maths when I heard this

4th way: inequality of means. Take the 99th root of both terms. The result for 50^99 is just 50. For 99!, you write that the geometric mean is strictly less than the arithmetic mean which is (1+2+3+...+99)/99 = 50. Therefore, 99th root of 99! is less than 99th root of 50^99, so once you raise everything to power 99, you get that 99! < 50^99.

Instead of induction, it's also simple to apply the first method to a general case. With the pairing off of m^2/((m-d)(m+d)) terms all being less than 1. where midpoint m=(n+1)/2, and differences d are in a range starting at 1 for odd n, or 0.5 for even n, with step size 1, and ending at m-1. You can easily see m^2>(m-d)(m+d) by geometry or by difference of two squares: (m-d)(m+d)=m^2-d^2.

For general solution, you can also take the natural log of each hand and use the Jensen inequality for natural log of x.

Isn't it easier to use (n+k)*(n-k) =n^2-k^2

@DavidSmyth666

3 жыл бұрын

Nice observation. This way you don’t need to do the whole induction proof

@DylanNelsonSA

3 жыл бұрын

Isn't this essentially the first way that he showed us?

@darkshoxx

3 жыл бұрын

@@DylanNelsonSA yeah, with proof by example, very hand-wavy

Your subscribers have grown rapidly When i subscribed you, you were at 36 k

@goodplacetostop2973

3 жыл бұрын

Michael will reach the 100K subs in December. I’d love to see him with the silver button from YT.

Just what I was looking for, encountered a similar problem today . Thank you

Excelent explanation Prof. Penn. I admire You and I always follow You. Thank you.

I actually solved this question with the simple method as we know that for every positive integer x, x² is greater than (x+y)(x-y) where y is any positive integer.

@BlacksmithTWD

3 жыл бұрын

Except when y = 0 of course. we can even tell how much greater/more using the formula: x^2 = (x+y) (x-y) + y^2 Don't these rules apply to negative integers for x as well? (-2)^2 > (-2+1) (-2 - 1) at least as long as x and y are both elements of Z it seems to work.

@petrospatrianakos9166

3 жыл бұрын

x^2 > (x+y)(x-y) because 0 > -y^2 (for y not equal to 0) x^2 > x^2 - y^2 x^2 > (x - y)(x + y). It applies for every x,y belonging to r, there are no restrictions except from y must not equal to 0, like Blacksmith said

@BlacksmithTWD

3 жыл бұрын

@@petrospatrianakos9166 I take it you meant -y^2>0 (for y not equal to 0), or did you mean 0 > -(y^2) for any y not equal to 0? (notation methods tend to change over the years and my way may have been outdated by now :) though if one exchanges the > symbolfor a >= symbol (not sure how to type greater than or equal to symbol on a qwerty keyboard), then even y = 0 works. since if y = 0 then (x+y) (x-y) = x^2 so then it boils down to x^2 >= x^2 which is correct. any real number not equal to 0 for y gives an y^2 > 0 in the formula x^2 = (x+y) (x-y) + y^2 any real number for y gives an y^2 >= 0

@petrospatrianakos9166

3 жыл бұрын

@@BlacksmithTWD -y^2 is smaller or equal to 0, since any number squared is a non-negative number (not sure how it is called in english), and since it has a minus in front of it, it is a non-positive number (negative or 0). So you can either say 0 > -y^2 x^2 > x^2 - y^2 x^2 > (x - y)(x + y) (for y not equal to 0) or say 0 >= -y^2 x^2 >= x^2 - y^2 x^2 >= (x - y)(x + y) for every y, and the equality is true when y=0.

@petrospatrianakos9166

3 жыл бұрын

But x and y can be any number, not just a positive integer and y is not necessarily smaller than x like the original comment suggested.

Me at 3 am need to sleep when there is school tomorrow: Let's watch this cause why not

Such an amazing way to easily sovle the problem.

For a fourth method for comparing x=((n+1)/2)^n and y=n! we can calculate ln(x) and ln(y) where the latter is approximated using Stirling's approximation to O(ln(n))

Me after failing honor precalc test: Im gonna study hard for next test Also me at mid night: 50^99 or 99! well let's figure it out

@skrimmtv3891

3 жыл бұрын

Bruh same i have 81 rn

I thought the cheating way is to compare 2^3 and 3! 😂

@FairArc

3 жыл бұрын

Uh

@hasndsome

3 жыл бұрын

But you have to prove the method 2 first to ensure that it works in this case.

@BlacksmithTWD

3 жыл бұрын

I wouldn't call that method cheating. Especially if you also compared 4^5 with 5!, 6^7 with 7!, 8^9 with 9! and pointed out the emerging pattern to derrive the conclusion that 50^99 > 99!.

@user-vv4zy9ss5s

3 жыл бұрын

@@BlacksmithTWD I think is to compare 3^5 with 5! , 4^7 with 7! , 5^9 and 9! It can be easily understood by the equation (x+y)(x-y)=x^2-y^2 less than x^2. For example, 99×1

@BlacksmithTWD

3 жыл бұрын

@@user-vv4zy9ss5s My bad, I was too hasty, the comparisons are when considering in an even number n as follows : n^(2n-1) with (2n-1)! so that would give us 2^3 with 3!, 4^7 with 7!, 6^11 with 11! etc.

You are amazing with math!!! Congratulations from Mexico

I subscribed because of this video. Great, man!

1:44 49+49=98, 98+1=50 🤔😉

I honestly thought, that for the "cheating" way he'd just take out his calculator

@SadisticNiles

3 жыл бұрын

The calculator gives up for factorials bigger than 69!

@apolloniuspergus9295

3 жыл бұрын

Mine goes up to 170!

@ZipplyZane

3 жыл бұрын

@@SadisticNiles It all depends on what the maximum value your calculator can hold. The difference is large enough that any rounding is irrelevant.

@SadisticNiles

3 жыл бұрын

@@ZipplyZane true, but I would guess that for most standard calculators that limit is e100.

@ZipplyZane

3 жыл бұрын

@@SadisticNiles Yeah. I was actually thinking of the graphing calculator I used in math classes. I don't remember where it maxed out, but it was over e100. It wouldn't surprise me if it just used 64-bit floats, which max out around e300.

Forth way: Use log10 (This can be helpful for very large numbers or powers) Let the symbols be: (n^x, x!) Your program should be: double a = 0.0, b = 0.0; for(int i=0; i

Hi Michael, fun video! As a former physicist/applied-mathematician I like to see the actual numbers to get a feel for them. So your "cheat" method today was most welcome.

1:44 "49 + 49 is 98, +1 is 50"

@matthewlockard6599

3 жыл бұрын

Referring to the 50 in the middle

@nickcampbell3812

3 жыл бұрын

@@matthewlockard6599 I know, I'm just teasing.

Thats the kind of question we get in JEE where we don't even have enough time .

@shresthshukla6239

3 жыл бұрын

we dont get these😂😉😉🙂

Professor Penn, do you have or are you planning to do a series on Lp spaces? And finally I enjoyed this video keep up the good work

I was thinking about a problem like this the other day, just in two dimensions. If you’ve taken calc 2 you might know that in order to maximize area of a rectangle of fixed perimeter, you choose a square. This extends beautifully into this problem, which is essentially the same in 99 dimensions. We have 99 factors in both products, and to pick the greatest “volume”, we should choose the “square”, i.e. 50^99.

@Yougottacryforthis

Жыл бұрын

exactly, its congruent to simple max-min problems

There is another approach for the general case: use AM-GM inequality. (99!) ^(1/99) Watch out: the inequality is strict because involved numbers are different!

I started panicking when I saw there was hardly a minute for the video to end and he didn’t start to explain the cheating method.

@tanvisorout1217

3 жыл бұрын

Nice one xp

This man deserves more support

That was really unexpected ending but that made my day. 😂😂

This probably falls under cheating as well, but it got me the answer. The geometric mean of ninety-nine 50's is easy to calculate, it's 50. The geometric mean of the integers 1 through 99 is less than its arithmetic mean and is therefore less than 50. Since both terms can be rewritten as (geometric mean)^99, 50^99 must be bigger since it has the larger geometric mean.

@Merlin1908

3 жыл бұрын

Definitely isn’t cheating. It’s using AM-GM smartly to prove the general case in a more insightful way than the induction.

@spacescopex

2 жыл бұрын

Better method: kzread.info/dash/bejne/fZ2e2Lh_cdieh6w.html （2 topics included）

huuunm [ (50-n)*(50+n)=50² - n² ] 50² > 50² - n²

@RS-do2rb

3 жыл бұрын

Me too

Great lecture! I could understand both intuitively and strictly.

@spacescopex

2 жыл бұрын

七地さん？ MY SOLUTIONS: kzread.info/dash/bejne/h66B27iRg5O-fco.html kzread.info/dash/bejne/dJyom7dumpqclrw.html

I guess you can easiliy generalize the "simple" way too: The middle fraction n / n cancels out, and then you can group the remaining terms into n*n / (n-a)(n+a) for all a < n , and clearly (n-a)(n+a) = n^2 - a^2 is smaller than n*n.

For the 'cheating' way, I thought you were going to apply the Stirling approximation for n!. Even though it is 'only' an approximation there are bounds on the error term in the approximation that I'd expect to be able to use to turn the argument into a rigorous proof. Haven't actually worked this out on paper.

@JakkuSakura

3 жыл бұрын

I believe that MMA has magic to deal with precision

This is funny, my wife asked me the same question a few days ago! Fun video, thanks Michael. I think the simple explanation should be simpler. I answered the question in my head by thinking 9 * 11 < 100, done! That implies that 49*51

@spacescopex

2 жыл бұрын

Better method: kzread.info/dash/bejne/fZ2e2Lh_cdieh6w.html （2 topics included） That is what I am saying.

Love from the UK 👍, I know they're not really your 'style' of problem but MAT is an exam for students in the uk for university entrance maybe you could do one of those problems (some of my faves are 2019 q5, 2018 q4, 2017 q5) like this so Michael sees !!! Love the content

The end was just mind blowingly amazing... I laughed so hard... Thank you sir!

@spacescopex

2 жыл бұрын

MY SOLUTIONS: kzread.info/dash/bejne/h66B27iRg5O-fco.html kzread.info/dash/bejne/dJyom7dumpqclrw.html

I love induction because it’s like answering “Why is this true?” with “Because math says so”

@Joefrenomics

2 жыл бұрын

… You’re just showing the previous case implies the current case. Nothing fancy.

This is a quick numerical way someone could do on their calculator: Take ln() of both sides, so we have 99*ln(50) and ln(99*98*...*2*1) = Sum from k=0 to k=99 of ln(k). This way, one could raise both sides to the power of e after computing numerical values and tell by how much one side is greater than the other! :)

I used the Sterling approximation and prime factorizing both sides (with the approximation that 3 ~ e) in order to give a back of the envelope argument that 50^99 is bigger.

@englishmuffinpizzas

2 жыл бұрын

Was looking for this in the comments! I did this as well and it leads to a nice intuition for when this is true and an estimation of the ratio of the two numbers

Just posting a comment before it hits again in everyone's recommendation

The simple method is actually obvious. Why the complicated "general" method? Basically every term over there is 50*50/(50 - x)(50 + x) which is 50^2/(50^2 - x^2) which is always >= 1. QED

The square is the rectangular shape with the maximal area given a fixed perimeter (it would be a circle if we consider any shape). Meaning that a rectangle with sides 50x50 has a greater area than a rectangle with sides 51x49, 52x48, 53x47, ..., 99x1, all of which are rectangles with the same perimeter as the square of side length 50. This can also been seen in 50^2 > (50+c)(50-c) for non-zero c (and equal for c=0), because (50-c)(50+c) = 50^2 - c^2.

3:00 love how he says davaide

My way was faster, easier and just as reliable! I basically went "idk 50^99 just feels bigger" and, clearly, I was right

1:48 :"Notice 49+49=98+1=50" ExCuSe Me WtF?!! 😂😂

@matthewlockard6599

3 жыл бұрын

Referring to the 50 in the middle, the 98th exponent + 1 is 50.

Many thanks for this very good video.

Hope to like every new videos to support your channel :D

"98 + 1 is 50" Hmmm, is it?

Just a quick note guys: relying blindly on a software without any proof is very dangerous. :D

@troublemonkey1_626

3 жыл бұрын

I'm pretty sure I can trust wolfram alpha

That ending troll was excellent 😆

I'm in love with the third method.

Happy diwali

50^99 > 99!

It is even simpler to show, that (a-1)*a*(a+1) = a^3 - a 0). ==> 49*50*51 < 50*50*50, 48*49*50*51*52 < 50^5 and so on

A great video indeed 😁 Thanks ❤️

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