y'=[2x(1-x)+x^2]/(x-1)^2=(2x-x^2)/(x-1)^2y''=[(2-2x)(x-1)^2-(2x-x^2)*2(x-1)]/(x-1)^4= -2/(x-1)^3
y=x^2/(1-x)＝(x^2-1+1)/(1-x)=-1-x+1/(1-x)y'=-1+1/(1-x)^2y''=2/(1-x)^3
