Question

cho 2 da thuc :f(x)=-x^3+3x^2+4x

                        g(x)=2x^3-8x^2-2x

tim x de f(x)+g(x)=0

Answer 1

Ta có:
\(f\left(x\right)+g\left(x\right)=\left(-x^3+3x^2+4x\right)+\left(2x^3-8x^2-2x\right)\\ =-x^3+3x^2+4x+2x^3-8x^2-2x\\ =\left(-x^3+2x^3\right)+\left(3x^2-8x^2\right)+\left(4x-2x\right)\\ =x^3+\left(-5x^2\right)+2x\\ =x^3-5x^2+2x\)

Để \(f\left(x\right)+g\left(x\right)=0\) thì:
\(x^3-5x^2+2x=0\\ \Leftrightarrow x\left(x^2-5x+2\right)=0\)

\(\Leftrightarrow...\)