dz/dx=(-1/1+x^2)*(1/2y*(x^(1/2))
dz/dy=(-1/1+x^2)*(-x^(1/2)/y^2




d2z/dx2=(2x/(1+X^2)^2) *(1/2*Y*X^(1/2))- (1/(1+X2)) * (1/4Y*x^(1/2) )

не совсем уверенна в (1/2y*(x^(1/2))`