隐函数求导 1/(x^2+y^2)*[2x+2yy']=1/(1+x^2/y^2)*1/y*(-x/y^2)*y'
2xy+2y^2y'=-xy' y'=-2xy/(2y^2+x)
再对x求导 2y+2xy'+4y(y')^2+2y^2y''=-y'-xy''
y''=-(y'+2y+2xy'+4y(y')^2)/(x+2y^2)
在把y'=-2xy/(2y^2+x)带入就好了
隐函数求导 1/(x^2+y^2)*[2x+2yy']=1/(1+x^2/y^2)*1/y*(-x/y^2)*y'
2xy+2y^2y'=-xy' y'=-2xy/(2y^2+x)
再对x求导 2y+2xy'+4y(y')^2+2y^2y''=-y'-xy''
y''=-(y'+2y+2xy'+4y(y')^2)/(x+2y^2)
在把y'=-2xy/(2y^2+x)带入就好了