Factorise : 49(x−y)2−9(2x+y)2
49(x−y)2−9(2x+y)2=[7(x−y)]2−[3(2x+y)]2=(7x−7y)2−(6x+3y)2=(7x−7y+6x+3y)(7x−7y−6x−3y)=(13x−4y)(x−10y)