(x+3)²-x²=x²+6x+9-x²=6x+9 （x+y）²（x-y）²=[(x+y)(x-y)]²=(x²-y²)²=x的4次方-2x²y²+y的4次方 （x-2y+3z）（x+2y-3z）=[x-(2y-3z)][x+(2y-3z)]=...