a, \(=\left(x-2y\right)\left(x+2y\right)-2\left(x+2y\right)\)
\(=\left(x+2y\right)\left(x-2y-2\right)\)
b,\(=x^4-2x^2+2x^3-4x+2x^2-4\)
\(=x^2\left(x^2-2\right)+2x\left(x^2-2\right)+2\left(x^2-2\right)\)
\(=\left(x^2+2x+2\right)\left(x^2-2\right)\)
c, \(=x^2\left(x+2y\right)-\left(x+2y\right)\)
\(=\left(x^2-1\right)\left(x+2y\right)\)
d, \(=3\left(x^2-y^2\right)-2\left(x-y\right)^2\)
\(=3\left(x-y\right)\left(x+y\right)-2\left(x-y\right)^2\)
\(=\left(x-y\right)\left(3\left(x+y\right)-2\left(x-y\right)\right)\)
\(=\left(x-y\right)\left(3x+3y-2x+2y\right)\)
\(=\left(x-y\right)\left(x+5y\right)\)
e, \(=x^2\left(x-4\right)-9\left(x-4\right)\)
\(=\left(x^2-9\right)\left(x-4\right)\)
\(=\left(x-3\right)\left(x+3\right)\left(x-4\right)\)
f, \(=\left(x-y\right)\left(x+y\right)-2\left(x+y\right)\)
\(=\left(x+y\right)\left(x-y-2\right)\)
