(x^2+x-12/2-x-x^2)^2*(x^2-3x+2/x^2+5x+4)/(x^2-5x+6/x^2+3x+2)

括号里的二次多项式分别化成（x+a)(x+b)形式再约分.
分数线上方是[(x+4)(x-3)]^2*(x-1)(x-2)*[(x+1)(x+2)]^2
下方是[(x-1)(x+2)]^2*(x+1)(x+4)*[(x-2)(x-3)]^2
约分后上面剩(x+1)(x+4),下面剩(x-1)(x-2)
乘开就好了.