(x²-9)(9-x²)请写出过程,

(x²-9)(9-x²)请写出过程,

(x²-9)(9-x²)
=9x²-x的4次方-81+9x²
=-x的4次方+18x²-81

(x²-9)(9-x²)=-(x²-9)(x²-9)=-(x²-9)²

原式=-(x²-9)²=-x^4+18x²-81
如果是因式分解，原式=-(x+3)²(x-3)²