Factorise:
x2−y2−4xz+4z2
x2−y2−4xz+4z2=x2−4xz+4z2−y2=(x)2−2×x2z+(2z)2−(y)2=(x−2z)2−(y)2=(x−2z+y)(x−2z−y)=(x+y−2z)(x−y−2z)
Factorise: x2−y2+6y−9
Factorise: x2+y2−z2−2xy