9(x+2y)的2次方-25(x-2y)的2次方=?(8x-4y)(-2x+16y) =-8(2x-y)(x-8y)这一

9(x+2y)的2次方-25(x-2y)的2次方=[3(x+2y)+5(x-2y)][3(x+2y)-5(x-2y)]=(3x+6y+5x-10y)(3x+6y-5x+10y)=(8x-4y)(16y-2x)=8(2x-y)(8y-x)=-8(2x-y)(x-8y) 再问： 为什么(8x-4y)(16y-2x)=8(2x-y)(8y-x) 再答： (8x-4y)(16y-2x) =4(2x-y)*2(8y-x) =8(2x-y)(8y-x) =-8(2x-y)(x-8y) 把常数的公因数提取出来