3.=(x+9)/(x+3)+(X-3)/(X+3)=(2x+6)/(x+3)=2
4.=(2-x)/(x-1)除以(x^2-4)/(x-1)=-1/(x+2)
5.=(3-1)+1-9=-6
6.=-2-2+1+1/8=-23/8