Câu b : \(x^3+5x^2+8x+4\)
\(=x^3+2x^2+3x^2+6x+2x+4\)
\(=x^2\left(x+2\right)+3x\left(x+2\right)+2\left(x+2\right)\)
\(=\left(x+2\right)\left(x^2+3x+2\right)\)
\(=\left(x+2\right)\left[x^2+x+2x+2\right]\)
\(=\left(x+2\right)\left[x\left(x+1\right)+2\left(x+1\right)\right]\)
\(=\left(x+2\right)\left(x+1\right)\left(x+2\right)\)
\(=\left(x+1\right)\left(x+2\right)^2\)
Câu c : \(x^3-9x^2+6x+16\)
\(=x^3+x^2-10x^2-10x+16x+16\)
\(=x^2\left(x+1\right)-10x\left(x+1\right)+16\left(x+1\right)\)
\(=\left(x+1\right)\left(x^2-10x+16\right)\)
\(=\left(x+1\right)\left(x^2-2x-8x+16\right)\)
\(=\left(x+1\right)\left[x\left(x-2\right)-8\left(x-2\right)\right]\)
\(=\left(x+1\right)\left(x-2\right)\left(x-8\right)\)