Let 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:
f ( 1 ) = 0
the roots of g ( x ) are squares of the roots of f ( x ) .
Find the value of S = a 2 0 1 6 + b 2 0 1 6 + c 2 0 1 6 .
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Though Khang Nguyen Thanh's solution is the best,here is another approach which is a little TROLL and objective.
We know that any integer to the power 2016 is always positive.
If any of a , b , c is either ≤ − 2 or ≥ 2 then a 2 0 1 6 + b 2 0 1 6 + c 2 0 1 6 = 2 2 0 1 6 + s o m e t h i n g p o s i t i v e
Since such an huge answer cannot be entered in Brilliant answer box,we now have to check for the values 0 , 1 , − 1 . But since c = 0 , c 2 0 1 6 = 1 .
Hence this rules out 0 as an answer.Now the answers can only be 1 , 2 , 3 which can be easily done since we get 3 tries.
Thus when you enter 3 as your answer,you get CORRECT
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Note that g ( 1 ) = f ( 1 ) = 0 , so 1 is a root of both f ( x ) and g ( x ) .
Let p and q be the other two roots of f ( x ) , so p 2 and q 2 are the other two roots of g ( x ) .
We then get p q = − c and p 2 q 2 = − a , so a = − c 2 .
Also, ( − a ) 2 = ( p + q + 1 ) 2 = p 2 + q 2 + 1 + 2 ( p q + p + q ) = − b + 2 b = b .
Therefore b = c 4 .
Since f ( 1 ) = 0 we therefore get 1 + c − c 2 + c 4 = 0 .
Factorising, we get ( c + 1 ) ( c 3 − c 2 + 1 ) = 0 .
Note that c 3 − c 2 + 1 = 0 has no integer root and hence c = − 1 , b = 1 , a = − 1 .
Therefore S = a 2 0 1 6 + b 2 0 1 6 + c 2 0 1 6 = 3 .