a: \(=\left(x^2+x+1\right)\left(x^2+x+2\right)\)
b: \(=\left(x^2+3x\right)\left(x^2+3x+2\right)+1\)
\(=\left(x^2+3x\right)^2+2\left(x^2+3x\right)+1\)
\(=\left(x^2+3x+1\right)^2\)
c: \(=\left(x^2+1\right)^2+4x\left(x^2+1\right)+4x^2\)
\(=\left(x^2+2x+1\right)^2=\left(x+1\right)^4\)
d: \(=\left(x^2+5x+4\right)\left(x^2+5x+6\right)-24\)
\(=\left(x^2+5x\right)^2+10\left(x^2+5x\right)\)
\(=x\left(x+5\right)\left(x^2+5x+10\right)\)