Question

Thực hiện phép tính

(x-1)(x+1)(x+2)

Answer 1

(x-1)(x+1)(x+2)

\(=(x^2-1)\left(x+2\right)\)

\(=x^3+2x^2-x-2\)

Answer 2

Dùng hằng đẳng thức: \(a^2-b^2=\left(a-b\right)\left(a+b\right)\)

có:(x-1)(x+1)(x+2)=\(\left(x^2-1\right).\left(x+2\right)=\left(x^3-x\right)+\left(2x^2-2\right)=x.\left(x^2-1\right)+\left(2x^2-2\right)=x.\left(x^2-1\right)+2.\left(x^2-1\right)=\left(x^2-1\right).\left(x+2\right)\)