9(X+2Y)²-4(X-Y)²=[3(X+2Y)]²-[2(X-Y)]²=[3(X+2Y)+2(X-Y)][3(X+2Y)-2(X-Y)]=[3X+6Y+2X-2Y][3X+6Y-2X+2Y]=(5X+4Y)(X+8Y)
