\(x^3+6x^2-13x-42\)
\(=x^3-3x^2+9x^2-27x+14x-42\)
\(=x^2\left(x-3\right)+9x\left(x-3\right)+14\left(x-3\right)\)
\(=\left(x-3\right)\left(x^2+9x+14\right)\)
\(=\left(x-3\right)\left(x^2+7x+2x+14\right)\)
\(=\left(x-3\right)\left(x+7\right)\left(x+2\right)\)
Chúc bạn học tốt!!!