f ( x ) = x 3 + a x 2 + b x + c and g ( x ) = x 3 + b x 2 + c x + a , where a , b , c are integers with c = 0 . Suppose that the following conditions hold: (a) f ( 1 ) = 0 ; (b) the roots of g ( x ) = 0 are the squares of the roots of f ( x ) = 0 . Find the value of a 2 0 1 3 + b 2 0 1 3 + c 2 0 1 3 .
Let
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Very neat solution, upvoted !
@Parth Lohomi you have also posted this question before.
Good one,upvoted!
considering the roots of f(x)=0, as p,q and r- we see the roots of g(x)=0 as 1/p, 1/q and 1/r. Also, i) p+q+r=-1 ii) 1/p, 1/q and 1/r is same as p^2, q^2 and r^2. iii) fact that pqr is not 0. two of them are -1 and remaining is 1.
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So c = − ( a + b + 1 ) . Then f ( x ) = ( x − 1 ) ( x 2 + ( a + 1 ) x + ( a + b + 1 ) ) and g ( x ) = ( x − 1 ) ( x 2 + ( b + 1 ) x − a ) Let 1 , u , v be the roots of f . It follows − ( b + 1 ) = u 2 + v 2 = ( u + v ) 2 − 2 u v = ( a + 1 ) 2 − 2 ( a + b + 1 ) , whence b = a 2 , and − a = u 2 v 2 = ( a + b + 1 ) 2 , whence a = − c 2 . It follows 0 = 1 + a + b + c = 1 − c 2 + c 4 + c = ( c + 1 ) ( c 3 − c 2 + 1 ) , whence c = − 1 , and so a = − 1 and b = 1 . Therefore a 2 0 1 3 + b 2 0 1 3 + c 2 0 1 3 = − 1