x3+6x2+7x-2
=x3+2x2+4x2+8x-x-2
=(x+2)(x2+4x-1)
=(x+2)(x2+4x+4-5)
=(x+2)(x+2-√5）(x+2+√5）额，辛苦了。(x+2)(x2+4x-1)这一步是怎样得出的？x3+6x2+7x-2=【x3+2x2】+【4x2+8x】-【x+2】=(x+2)(x2+4x-1)