\(5x^2-10x+5=5\left(x^2-2x+1\right)=5\left(x-1\right)^2\)
\(x^2y-xy^2-3x+3y=xy\left(x-y\right)-3\left(x-y\right)=\left(x-y\right)\left(xy-3\right)\)
\(4x^2+4x+1-y^2=\left(2x+1\right)^2-y^2=\left(2x+1+y\right)\left(2x+1-y\right)\)
\(x^2-5x+6=x^2-2x-3x+6=x\left(x-2\right)-3\left(x-2\right)=\left(x-2\right)\left(x-3\right)\)