\(a,x^2-2x-4y^2-4y\)
\(=\left(x^2-4y^2\right)-\left(2x+4y\right)\)
\(=\left(x-2y\right)\left(x+2y\right)-2\left(x+2y\right)\)
\(=\left(x+2y\right)\left(x-2y-2\right)\)
\(b,2x+2y-x^2-xy\)
\(=\left(2x-x^2\right)+\left(2y-xy\right)\)
\(=x\left(2-x\right)+y\left(2-x\right)\)
\(=\left(x+y\right)\left(2-x\right)\)