a: \(7x+7xy=7x\left(y+1\right)\)
b: \(2x^2y-6xy^2=2xy\left(x-3y\right)\)
c: \(3x\left(x-1\right)+7x^2\left(x-1\right)=x\left(x-1\right)\left(3+7x\right)\)
d: \(x^2-6xy+9y^2=\left(x-3y\right)^2\)
e: \(x^2-64=\left(x-8\right)\left(x+8\right)\)
f: \(3x\left(x-a\right)+5a\left(a-x\right)=\left(x-a\right)\left(3x-5a\right)\)