2X^3 +7x - 9 = 0

问题描述:

2X^3 +7x - 9 = 0
二X的三次方减去七X减去9=0
怎么用十字相乘?

没有办法用十字相乘法
拆和凑
7x-7+2x^3-2=
7(x-1)+2(x^3-1)
=7(x-1)+2(x-1)(x^2+x+1)
=(x-1)(7+2x^2+2x+2)
=(x-1)(2x^2+2x+9)
x=1