(2x-6)除以(X平方-4x+4)除以(x+3)乘以(x平方+x-6)除以(12-4x)
=2(x-3)/(x-2)^2/(x+3)*(x+3)(x-2)/4(3-x)
=-2(x-3)/[(x-2)^2*(x+3)]*(x+3)(x-2)/4(x-3)
=-1/2(x-2)