a. \(x^2-2x+2y-xy=\left(x^2-2x\right)-\left(xy-2y\right)=x\left(x-2\right)-y\left(x-2\right)=\left(x-2\right)\left(x-y\right)\)
b. \(x^2+4xy-16+4y^2=\left(x^2+4xy+4y^2\right)-16=\left(x+2y\right)^2-4^2=\left(x+2y-4\right)\left(x+2y+4\right)\)
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