两边对x求导：3x^2+3y^2 y'-3y-3xy'=0即x^2-y=xy'-y^2y'=(x^2-y)/(x-y^2)
两边对x求导得3x^2+3y^2y'-3y-3xy'=0y'=(x^2-y)/(x-y^2)
