a: \(125-x^6=\left(5-x^2\right)\left(5+5x^2+x^4\right)\)
b: \(=\left(x^2+1-3\right)^2=\left(x^2-2\right)^2\)
c: \(=\left(3x+15\right)^2-\left(x+7\right)^2\)
\(=\left(3x+15+x+7\right)\left(3x+15-x-7\right)\)
\(=\left(4x+22\right)\left(2x+8\right)\)
\(=2\left(2x+1\right)\left(x+4\right)\)
d: \(=9-\left(x-y\right)^2\)
\(=\left(3-x+y\right)\left(3+x-y\right)\)
e: \(=x\left(x^2+2xy+y^2-9\right)\)
\(=x\left(x+y-3\right)\left(x+y+3\right)\)