y'=1/√(1-x^2)+(1-x^2)^(-1.5)*(-2x)=(1-x^2)^(-1.5)*(1-x^2-2x)y"=(-2x-2)*(1-x^2)^(-1.5)+(1-x^2-2x)*(1-x^2)^(-2.5)(-2x)=(1-x^2)^(-2.5)*[(-2x-2)*(1-x^2)+(1-x^2-2x)*(-2x)]合并同类项即可
