16(x+y)²-25﹙x-y﹚²

16(x+y)²-25﹙x-y﹚²

=[4(x+y)]²-[5(x-y)]²
=[4(x+y)+5(x-y][4(x+y)-5(x-y)]
=(9x-y)(-x+9y)
=-(9x-y)(x-9y)
計算:=-9x²+82xy-9y²