Find the sum of all integral roots of the equation 6 x 6 − 2 5 x 5 + 3 1 x 4 − 3 1 x 2 + 2 5 x − 6 = 0
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Obviously x = 0 is not a solution of the given equation. So dividing both sides of the equation by x 3 we obtain the equivalent equation 6 x 3 − 2 5 x 2 + 3 1 x − x 3 1 + x 2 2 5 − x 3 6 = 0 . Rearranging terms we get 6 ( x 3 − x 3 1 ) − 2 5 ( x 2 − x 2 1 ) + 3 1 ( x − x 1 ) = 0 . Factoring x − x 1 out we get ( x − x 1 ) ( 6 ( x 2 + x 2 1 + 1 ) − 2 5 ( x + x 1 ) + 3 1 ) = 0 . The latter equation can be rewritten as ( x − x 1 ) ( 6 ( x + x 1 ) 2 − 2 5 ( x + x 1 ) + 2 5 ) = 0 . Therefore we get that x − x 1 = 0 , x + x 1 = 3 5 , and x + x 1 = 2 5 . Solving these three equations we get that the solutions are 1 , − 1 , 2 , 2 1 , 6 5 + i 1 1 , and 6 5 − i 1 1 . Therefore the sum of the integer roots is 1 + ( − 1 ) + 2 = 2 .
Used the same method.
nice method
Using trial and error (use the factors of 6) , we get x=1,or -1,
6x^6 – 25x^5 + 31x^4 – 31x^2 + 25x – 6 = (x^2 – 1)(6x^4 - 25x^3 + 37x^2 - 25x + 6) =0
Repeat again, then x=2, So (6x^4 - 25x^3 + 37x^2 - 25x + 6) = (x – 2)(6x^3 - 13x^2 + 11x – 3) = 0
Also x=1/2,is the solution of (6x^3 - 13x^2 + 11x – 3) = (2x – 1)(3x^2 - 5x +3) = 0.So the sum of integral roots = 1 - 1 + 2 = 2
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6 x 6 − 2 5 x 5 + 3 1 x 4 − 3 1 x 2 + 2 5 x − 6 6 ( x 6 − 1 ) − 2 5 x ( x 4 − 1 ) + 3 1 x 2 ( x 2 − 1 ) 6 ( x 2 − 1 ) ( x 4 + x 2 + 1 ) − 2 5 x ( x 2 − 1 ) ( x 2 + 1 ) + 3 1 x 2 ( x 2 − 1 ) ( x 2 − 1 ) ( 6 x 4 − 2 5 x 3 + 3 7 x 2 − 2 5 x + 6 ) ( x 2 − 1 ) ( 6 x 4 − 1 2 x 3 − 1 3 x 3 + 2 6 x 2 + 1 1 x 2 − 2 2 x − 3 x + 6 ) ( x 2 − 1 ) ( 6 x 3 ( x − 2 ) − 1 3 x 2 ( x − 2 ) + 1 1 x ( x − 2 ) − 3 ( x − 2 ) ) ( x 2 − 1 ) ( x − 2 ) ( 6 x 3 − 1 3 x 2 + 1 1 x − 3 ) ( x 2 − 1 ) ( x − 2 ) ( 6 x 3 − 3 x 2 − 1 0 x 2 + 5 x + 6 x − 3 ) ( x 2 − 1 ) ( x − 2 ) ( 3 x 2 ( 2 x − 1 ) − 5 x ( 2 x − 1 ) + 3 ( 2 x − 1 ) ) ( x 2 − 1 ) ( x − 2 ) ( 2 x − 1 ) ( 3 x 2 − 5 x + 3 ) = 0 = 0 = 0 = 0 = 0 = 0 = 0 = 0 = 0 = 0
We note that 3 x 2 − 5 x + 3 = 0 has no real root, therefore the sum of integral real roots is 1 − 1 + 2 = 2