y'逗悄-xy'=1/2(y^2+y')y'(1-x)=1/2y^2+1/2y'y'(1/正蠢2-x)=1/2y^2y'(1-2x)=y^2dy/dx=y^2/(1-2x)1/举指陪y^2dy=dx/(1-2x)两边积分：-1/y=-1/2 * ln|1-2x|+C
