Question

\(\left(-x-2\right)^3\) + (2x-4)\(\left(x^2+2x+4\right)\) - \(x^2\)(x-6) tại x = -2

Answer 1

Đặt \(A=\left(-x-2\right)^3+\left(2x-4\right)\left(x^2+2x+4\right)-x^2\left(x-6\right)\)

\(=-\left(x+2\right)^3+2\left(x-2\right)\left(x^2+2x+4\right)-x^3+6x^2\)

\(=-x^3-6x^2-12x-8+2\left(x^3-8\right)-x^3+6x^2\)

\(=-2x^3-12x-8+2x^3-16=-12x-24\)

Khi x=-2 thì \(A=-12\cdot\left(-2\right)-24=24-24=0\)