2016 2016 2016

Algebra Level 3

201 6 x + 201 6 2 + 201 6 2 + + 201 6 2 2015 times 201 6 y = 2016 \frac{2016^x+\underbrace{2016^2+2016^2+\ldots+2016^2}_{2015 \text{ times}}}{2016^y}=2016

where x x and y y are both positive integers

What is the value of x 3 y 3 + 2016 x y 2016 x y \dfrac{x^3-y^3+2016xy}{2016xy} ?


The answer is 1.

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1 solution

Hung Woei Neoh
Jul 8, 2016

201 6 x + 201 6 2 + 201 6 2 + + 201 6 2 2015 times 201 6 y = 2016 201 6 x + 2015 ( 201 6 2 ) = 2016 ( 201 6 y ) 2015 ( 201 6 2 ) = 201 6 1 + y 201 6 x 2015 = 201 6 1 + y 201 6 x 201 6 2 2016 1 = 201 6 y 1 201 6 x 2 201 6 1 201 6 0 = 201 6 y 1 201 6 x 2 \dfrac{2016^x+\underbrace{2016^2+2016^2+\ldots+2016^2}_{2015\text{ times}}}{2016^y}=2016\\ 2016^x+2015(2016^2)=2016(2016^y)\\ 2015(2016^2)=2016^{1+y}-2016^x\\ 2015=\dfrac{2016^{1+y}-2016^x}{2016^2}\\ 2016-1=2016^{y-1}-2016^{x-2}\\ 2016^1-2016^0=2016^{y-1}-2016^{x-2}

Compare the terms, and we get

y 1 = 1 y = 2 x 2 = 0 x = 2 y-1=1 \implies y=2\\ x-2=0 \implies x=2

Therefore,

x 3 y 3 + 2016 x y 2016 x y = 2 3 2 3 + 2016 ( 2 ) ( 2 ) 2016 ( 2 ) ( 2 ) = 2016 ( 4 ) 2016 ( 4 ) = 1 \dfrac{x^3-y^3+2016xy}{2016xy}\\ =\dfrac{2^3-2^3+2016(2)(2)}{2016(2)(2)}\\ =\dfrac{2016(4)}{2016(4)}\\ =\boxed{1}

Great solution +1. I hope there's no another possible solution.

Novril Razenda - 4 years, 11 months ago

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