-x
[1+x-1/(1-x)]÷[x-x^2/(x-1)]=[(1+x)(1-x)/(1-x)]÷[x(x-1)-x^2]/(x-1)=[(1+x)(1-x)/(1-x)]÷(x^2-x-x^2)/(x-1)=[(1+x)(1-x)/(1-x)]×(x-1)/(-x)=(1-x^2)/(1-x)×(1-x)/x=(1-x^2)/x
图
