Inspired by Steven Zheng

Algebra Level 3

Let

S 0 = 1 2 8 + 1 4 8 + 1 6 8 + S_{0} = \frac{1}{2^{8}}+\frac{1}{4^{8}}+\frac{1}{6^{8}}+\ldots

S 1 = 1 1 8 + 1 3 8 + 1 5 8 + S_{1} = \frac{1}{1^{8}}+\frac{1}{3^{8}}+\frac{1}{5^{8}}+\ldots

If S 0 S 1 = a b \frac{S_{0}}{S_{1}} = \frac{a}{b} where a a and b b are coprime positive integers , what is the value of a + b ? a+b?


The answer is 256.

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5 solutions

U Z
Dec 31, 2014

S 0 = 1 2 8 ( 1 1 8 + 1 2 8 + 1 3 8 + . . . . . . . . . ) S_{0} = \dfrac{1}{2^8}( \dfrac{1}{1^8} + \dfrac{1}{2^8} + \dfrac{1}{3^8} + .........)

S 1 = 1 1 8 + 1 3 8 + 1 5 8 . . . . S_{1} = \dfrac{1}{1^8} + \dfrac{1}{3^8} + \dfrac{1}{5^8} ....

S 0 = 1 2 8 ( S 0 + S 1 ) S_{0} = \dfrac{1}{2^8}( S_{0} + S_{1})

S 0 S 1 = 1 2 8 ( S 0 S 1 + 1 ) \dfrac{S_{0}}{S_{1}} = \dfrac{1}{2^8}( \dfrac{S_{0}}{S_{1}} + 1)

a b = 1 2 8 1 \dfrac{a}{b} = \dfrac{1}{2^8 - 1}

a + b = 2 8 \boxed{a + b = 2^8}

i think i have stole your solution from your brain megh choksi because i've done in this same method... :P

Trishit Chandra - 6 years, 5 months ago

Exactly :) You should check out Steven's Books, they're full of awesome knowledge.

Jake Lai - 6 years, 5 months ago

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Isn't it great to be inspired by others? I love posting such questions :)

Calvin Lin Staff - 6 years, 5 months ago

Downloaded all

U Z - 6 years, 5 months ago

Where can you get his books?

Julian Poon - 6 years, 5 months ago

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Here it is

U Z - 6 years, 5 months ago

Same solution

Vishal S - 5 years, 7 months ago

problem is overrated

Aryan Gaikwad - 6 years, 2 months ago
Steven Zheng
Jan 2, 2015

So you got the inspiration from my books. No wonder why I don't remember posting a problem like this on Brilliant.

I actually used the method from my findings ζ ( n ) = 2 n 2 n 1 k = 1 1 ( 2 k 1 ) n . \zeta{(n)} = \frac{{2}^{n}}{{2}^{n}-1} \sum _{ k=1 }^{ \infty }{ \frac { 1 }{ { \left( 2k-1 \right) }^{ n } } } .

Yeah, it's full of great findings. Thanks for sharing :)

Jake Lai - 6 years, 5 months ago
Jason Hughes
Jan 15, 2016

S 0 = 1 2 8 + 1 4 8 + 1 6 8 + S_{0} = \frac{1}{2^{8}}+\frac{1}{4^{8}}+\frac{1}{6^{8}}+\ldots

S 1 = 1 1 8 + 1 3 8 + 1 5 8 + S_{1} = \frac{1}{1^{8}}+\frac{1}{3^{8}}+\frac{1}{5^{8}}+\ldots

2 8 S 0 = 1 1 8 + 1 2 8 + 1 3 8 + 2^8S_{0} = \frac{1}{1^{8}}+\frac{1}{2^{8}}+\frac{1}{3^{8}}+\ldots

2 8 S 0 S 0 = 1 1 8 + 1 3 8 + 1 5 8 + 2^8S_{0}-S_{0} = \frac{1}{1^{8}}+\frac{1}{3^{8}}+\frac{1}{5^{8}}+\ldots

2 8 S 0 S 0 = S 1 2^8S_{0}-S_{0} = S_{1}

( 2 8 1 ) S 0 = S 1 (2^8-1)S_{0} = S_{1}

S 0 S 1 = 1 2 8 1 \frac{S_{0}}{S_{1}}=\frac{1}{2^8-1}

a = 1 , b = 2 8 1 , a + b = 2 8 = 256 a=1, b=2^8-1, a+b=2^8=256

nice and easy to understand

Prakhar Dhumas - 5 years, 2 months ago
Curtis Clement
Jan 1, 2015

S 0 S_0 = 1 2 8 \frac{1}{2^8} [ 1 1 8 \frac{1}{1^8} + 1 2 8 \frac{1}{2^8} + 1 3 8 \frac{1}{3^8} +...] = n 2 8 \frac{n}{2^8} , where n {n} = i = 1 \displaystyle \sum_{i=1}^\infty 1 i 8 \frac{1}{i^8} . Now it is clear to see that n {n} = S 0 S_0 + S 1 S_1 , so S 0 S_0 = S 0 + S 1 2 8 \frac{S_0 + S_1}{2^8} . Rearranging gives: 255 S 0 S_0 = S 1 S_1 , so S 0 S 1 \frac{S_0}{S_1} = 1 255 \frac{1}{255} . \therefore a {a} + b {b} = 256

Anna Anant
Jan 15, 2015

So+S1 can be expressed as, Sum(n=1...infinity) (1/n^8), while So=Sum(n=1...infinity) [1/(2n)^8]=(1/2^8) Sum(n=1...infinity) (1/n^8). Therefore, (So+S1)/So=2^8=256, So+S1=256So, S1=255So. Therefore, So/S1=1/255, from which a=1 & b=255 so that a+b=256

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