因数分解① -x^6-7x^3+8② x^3-7x+6③ b^3+b^2-2急答对了再加分第①题=-(x³+8)(x³-1) 怎么来的

① -x^6-7x^3+8
=-(x^6+7x³-8)
=-(x³+8)(x³-1)
=-(x+2)(x²-2x+4)(x-1)(x²+x+1)
② x^3-7x+6
=x³-x-6x+6
=x(x²-1)-6(x-1)
=x(x+1)(x-1)-6(x-1)
=(x-1)(x²+x-6)
=(x-1)(x+3)(x-2)
③ b^3+b^2-2
=(b³-1)+(b²-1)
=(b-1)(b²+b+1)+(b+1)(b-1)
=(b-1)(b²+b+1+b+1)
=(b-1)(b²+2b+2)