x的平方-9分之1-x-3分之1除以x-1分之6+2x
=1/(x^2-9) - 1/(x-3) *(x-1)/2(3+x)
=(2- (x-1))/2(x^2-9)
=(3-x)/2(x^2-9)
=-(x-3)/2(x+3)(x-3)
=-1/2(x+3)