coefficient of a cubic expression

So the given cubic is $x^3-2x^2+ax+10=0$ . The condition is one of the root is additive inverse of another. I need to find the coefficient $a$ . I did some algebraic calculations and cancelling of the cubic terms and sqaure terms and got answer as $-25$ . Just want to know whether its right if not then please explain me how to approach such sums.