Factorise:
(x2+4y2−9z2)2−16x2y2
(x2+4y2−9z2)2−16x2y2=(x2+(2y)2−(3z)2)2−(4xy)2 , using identity (a2−b2)=(a+b)(a−b)=(x2+(2y)2−(3z)2−4xy)(x2+(2y)2−(3z)2+4xy)=(x2+(2y)2−4xy−(3z)2)(x2+(2y)2+4xy−(3z)2)=((x−2y)2−(3z)2)((x+2y)2−(3z)2)=[(x−2y−3z)(x−2y+3z)][(x+2y−3z)(x+2y+3z)]=(x−2y−3z)(x−2y+3z)(x+2y−3z)(x+2y+3z)