5x2-10xy+5y2-20z2
=5(x2-2xy+y2-4z2)
=5[(x2-2xy+y2)-4z2]
=5(x-y)2-(2z)2
=5(x-y+2z)(x-y-2z)
\(5x^2-10xy+5y^2-20z^2\)
\(=5\left(x^2-2xy+y^2-4z^2\right)\)
\(=5\left[\left(x^2-2xy+y^2\right)-\left(2z\right)^2\right]\)
\(=5\left[\left(x-y\right)^2-z^2\right]\)
\(=5\left(x-y-z\right)\left(x-y+z\right)\)