Art of Problem Solving: 2020 AMC 10 A #21 / AMC 12 A #19

Art of Problem Solving's Richard Rusczyk solves the 2020 AMC 10 A #21 / AMC 12 A #19.

[too_many_chromosomes]

Bruh 10 years ago this would of been on aime

[AdityaRaj-mjce]

Rusczyk is back.
Thanks for all your lessons. Earlier I had to wait for a month to watch you do math on Mathcounts channel.
Keep doing what are you doing, forever.

[anticorncob]

Holy crap I wasn’t expecting this to be out already.

[donaldbiden]

i sent him a friend request on AOPS, lets see how much time he takes to reject it XD

[eric]

You are the so funny richard. Also there is a typo it says a^k instead of a subscript k. You are the best richard

[didacticdudes]

This was perfectly explained, thank you so much!

[MathArts]

It confuses me that the k is power of a in your video, actually it is a's subscript.

[TechToppers]

I'm preparing from India. These extra problems help a lot.

[elonmusk]

Please do some questions of the Putnam test

[RedOctober_]

We're gonna need some *horrors* A-ALGEBRA...a lot of ALGEBRA

[jerrydai]

It's out already?
Wow!
Nice job!

[sriindla]

I answer 17 on the amc 12 and I already know I got 2 wrong. Do you think ill make AIME? What do you think will be the AMC 12 floor?

[ashc]

The intro's more modern but the hairstyle's still OG

[זאבגלברד]

You are using (a^n+b^n) / (a+b) , when n is odd , formula. You are also using the formula for sum of a geometric seria a1=1, q=2 Thanks for showing that !

[jacobgoldman]

how are there only 8 terms in left part of product instead of 15? It looks like the answer should be 256.

[solarrrrrrrrrrrrr]

How can I do really good on the AMC 10's?

[jerryli]

Typo: a^k should be a_k.

Great video anyway! :)

[lemon_kade]

i transfer them into base -2 and get 17 round to get 137. This algebra way is much faster

[RedOctober_]

All his steps are so logical, so simple but somehow i never come up with the solution on the real test ):

[wiellnyan]

Gotta not forget about that one.
Can we just write all of this in binary? Powers are annoying. Plus it is related to two.