2x+4/x^2;+6x+9 除以 x+2 乘以x^2;+x-6/8-4x
=2(x+2)/(x+3)^2*1/(x+2)*(x-2)(x+3)/4(2-x)
=1/(x+3)*(-1)
=-1/(x+3)
太简单了