Lời giải:
a.
$x^3+6x^2+11x+6$
$=x^3+x^2+5x^2+5x+6x+6$
$=x^2(x+1)+5x(x+1)+6(x+1)=(x+1)(x^2+5x+6)$
$=(x+1)(x^2+2x+3x+6)=(x+1)[x(x+2)+3(x+2)]$
$=(x+1)(x+2)(x+3)$
b.
$x^3-8x^2+x+42=(x^3+2x^2)-(10x^2+20x)+(21x+42)$
$=x^2(x+2)-10x(x+2)+21(x+2)$
$=(x+2)(x^2-10x+21)$
$=(x+2)(x-3)(x-7)$
a) Ta có: \(x^3+6x^2+11x+6\)
\(=x^3+x^2+5x^2+5x+6x+6\)
\(=x^2\left(x+1\right)+5x\left(x+1\right)+6\left(x+1\right)\)
\(=\left(x+1\right)\left(x+2\right)\left(x+3\right)\)
b) Ta có: \(x^3-8x^2+x+42\)
\(=x^3+2x^2-10x^2-20x+21x+42\)
\(=x^2\left(x+2\right)-10x\left(x+2\right)+21\left(x+2\right)\)
\(=\left(x+2\right)\left(x-3\right)\left(x-7\right)\)
