a) Ta có: \(x^3-x^2-4\)
\(=x^3+x^2+2x-2x^2-2x-4\)
\(=x\left(x^2+x+2\right)-2\left(x^2+x+2\right)\)
\(=\left(x^2+x+2\right)\left(x-2\right)\)
b) Ta có: \(3x^3+5x^2+8x+4\)
\(=3x^3+2x^2+3x^2+2x+6x+4\)
\(=x^2\left(3x+2\right)+x\left(3x+2\right)+2\left(3x+2\right)\)
\(=\left(3x+2\right)\left(x^2+x+2\right)\)