IMO qualification

Algebra Level 3

To different numbers, a and b fulfills these to equations.

x 2019 + a x + 2 b = 0 x^{2019} + ax+2b =0 and x 2019 + b x + 2 a = 0 x^{2019} + bx+2a =0

they have a common solution.

what are all possible values of a+b?

-4^2017 -2^2018 2 -2^2020

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1 solution

Neo Strecker
Feb 26, 2020

if x is a solution to both equations so is x to the equation we get for subtracting the last equation from the first. by doing this we get: a x b x + 2 b 2 a = 0 ax-bx+2b-2a =0 this equation is the same as ( a b ) x = 2 ( a b ) (a-b)x =2(a-b) because a and b are different we can divide by a-b≠0. this gives us x=2 now we just plug this value into one of the equations. 2 2019 + 2 a + 2 b = 0 2^{2019} + 2a+2b =0 where [a+b= 2 2019 2 \frac{ 2^{2019} }{-2} ] =[ -2^{2018}] hence the possible values of a+b are [ -2^{2018}]

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