1（x+3y)(x-3y)(x^2+9y^2) =(x^2-9y^2) (x^2+9y^2) =(x^4-81y^4)
（-3）^2n+1+3(-3)^2n
2是不是）（-3）^（2n+1）+3(-3)^2n=（-3）^（2n+1）-（-3）(-3)^2n=
（-3）^(2n+1)-(-3)^（2n+1）=0(x+y+z)(x-y-z)-(x-y+z)(x+y-z)比谁快谢谢(x+y+z)(x-y-z)-(x-y+z)(x+y-z)=(x+y+z)[x-(y+Z)]-[x-(y-z)][x+(y-z)]=x²-（y+z）²-x²+（y-z）²=（y-z）²-（y+z）²=（y-z-y-z）（y-z-y-z）=-2z*（-2z）=4z²