\(x^2-5x-y^2-5y=x^2-y^2-5x-5y=\left(x-y\right)\left(x+y\right)-5\left(x+y\right)=\left(x+y\right)\left(x-y-5\right)\)
\(x^3+2x^2-4x-8=x^2\left(x+2\right)-4\left(x+2\right)=\left(x^2-4\right)\left(x+2\right)=\left(x-2\right)\left(x+2\right)^2\)
\(a^3-8a^2+16a=a\left(a^2-8a+16\right)=a\left(a-4\right)^2\)


