(x^2+2x+4)(x^2+2x-3)-8
设m=x^2+2x+4
原式
=m(m-7)-8
=m^2-7m-8
=(m+1)(m-8)
=(x^2+2x+4+1)(x^2+2x+4-8)
=(x^2+2x+5)(x^2+2x-4)