为方便,记t=x+3f(x)=1/[(x+1)(x+2)]=1/(x+1)-1/(x+2)=1/(x+3-2)-1/(x+3-1)=1/(t-2)+1/(1-t)=-0.5/(1-t/2)+1/(1-t)=-0.5[1+t/2+(t/2)^2+...+(t/2)^n+...]+[1+t+t^2+...t^n+...]=0.5+t(1-1/4)+t^2(1-1/8)+.+t^n(1-1/2^...