12(x+y)²+11(x²-y²)+2(x-y)²
=12(x+y)²+11(x+y)(x-y)+2(x-y)²
=[3(x+y)+2(x-y)][4(x+y)+(x-y)]
=(3x+3y+2x-2y)(4x+4y+x-y)
=(5x+y)(5x+3y)