A Too Easy One in Fact!

Algebra Level 4

Let α \alpha and β \beta be the roots of the quadratic equation x 2 + x + 1 = 0 x^2+x+1 = 0 . If a , b a,b and c c are positive integers satisfying gcd ( a , b , c ) = 22 \gcd(a,b,c) = 22 such that the quadratic equation a x 2 + b x + c = 0 ax^2+bx+ c=0 has α 62 \alpha^{62} and β 62 \beta^{62} as its roots, find the value of a + b + c a+b+c .


The answer is 66.

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1 solution

Kay Xspre
Nov 23, 2015

With x 2 + x + 1 = 0 x^2+x+1 = 0 , we multiply x 1 x-1 for both sides, and gives x 3 1 = 0 x^3-1 = 0 . Now, since α 62 = ( 1 20 ) α 2 \alpha^{62} = (1^{20})\alpha^2 , and β 62 = ( 1 20 ) β 2 \beta^{62} = (1^{20})\beta^2 , we resolve for α , β \alpha, \beta , which gives α = 1 + i 3 2 ; β = 1 i 3 2 \alpha = \frac{-1+i\sqrt{3}}{2};\:\beta = \frac{-1-i\sqrt{3}}{2} and β 2 = α ; α 2 = β \beta^2 = \alpha;\: \alpha^2 = \beta , hence we will come to the same equation, the x 2 + x + 1 = 0 x^2+x+1 = 0 , where the g c d ( 1 , 1 , 1 ) = 1 gcd(1,1,1) = 1 , but since we require the equation with g c d ( a , b , c ) = 22 gcd(a,b,c) = 22 , we just multiply 22 into the original equation, which gives 22 x 2 + 22 x + 22 = 0 22x^2+22x+22 = 0 , hence, a + b + c = 22 + 22 + 22 = 66 a+b+c = 22+22+22 = 66

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