a: \(=9xy\left(y-2x\right)\)
b: \(=2\left(3x^2-y\right)\)
c: \(=7x\left(x-y\right)+14y\left(x-y\right)=7\left(x-y\right)\left(x+2y\right)\)
d: \(=\left(\sqrt{7}-x\right)\left(\sqrt{7}+x\right)\)
e: \(=\left(x+4\right)^2\)
f: \(=\left(1-3x\right)\left(1+3x+9x^2\right)\)
g: \(=\left(x-3\right)^3\)