b: \(=\left(x^2+x\right)^2+4\left(x^2+x\right)-12\)
\(=\left(x^2+x+6\right)\left(x^2+x-2\right)\)
\(=\left(x^2+x+6\right)\left(x+2\right)\left(x-1\right)\)
d: \(x\left(x+1\right)\left(x+2\right)\left(x+3\right)-8\)
\(=\left(x^2+3x\right)\left(x^2+3x+2\right)-8\)
\(=\left(x^2+3x\right)^2+2\left(x^2+3x\right)-8\)
\(=\left(x^2+3x+4\right)\left(x^2+3x-2\right)\)