Question

Bài 1: rút gọn 

\(\left(x^2-1\right).\left(x+2\right)-\left(x-2\right).\left(x^2+2x+4\right)\)

Answer 1

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

\(=x^3-2x^2-x-2-x^3+8\)

=\(-2x^2-2x-10\)

Answer 2

\(\left(x^2-1\right)\cdot\left(x+2\right)-\left(x-2\right)\cdot\left(x^2 +2x+4\right)\)

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

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

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

\(=\left(x+2\right)\cdot\left(x^2-1-x^2+4\right)\)

\(=\left(x+2\right)\cdot3=3x+6\)