（x²-1）（x+3）（x+5)-20
=(x+1)(x-1)(x+3)(x+5)-20
=(x+1)(x+3)(x-1)(x+5)-20
=(x²+4x+3)(x²+4x-5)-20
=(x²+4x)²-2(x²+4x)-15-20
=(x²+4x)²-2(x²+4x)-35
=(x²+4x-7)(x²+4x+5)初中答案
=(x+2+√11)(x+2-√11)(x²+4x+5)实数范围内分解因式
=(x+2+√11)(x+2-√11)(x+2+i)(x+2-i)复数范围内分解因式