(x-2y+3)^2
=[(x-2y)+3]²
=(x-2y)²+6(x-2y)+9
=x²-4xy+4y²+6x-12y+9 (x-2y+3)^2
=[(x-2y)+3]²
=(x-2y)²+6(x-2y)+9
=x²-4xy+4y²+6x-12y+9