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