(x^2-9)(x^2+9)-(9-x^2)^2

问题描述:

(x^2-9)(x^2+9)-(9-x^2)^2

(x²-9)(x²+9)-(9-x²)²
=(x²-9)(x²+9)-(x²-9) ²
=(x²-9)[x²+9-(x²-9)]
=(x²-9)(x²+9-x²+9)
=18(x²-9)
=18(x+3)(x-3)