# Formal implicit differentiation

As my question was poorly asked, I rewrite it.

I was searching for the code of first order and second order differentiation of an implicit function. Finally I found and post it.

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Here is the code for first and second order implicit differentiation of a two variables function

#Evaluation of the two first derivatives of an implicit function var("x, y, dx, dy, al, be") V=function('V')(x, y)# A) either A or B should be uncomment

# V= x^al*y^be# B)

V_x = diff(V, x) V_y = diff(V, y)

# Evaluation of the two first derivatives of an implicit function

var("x, y, dx, dy, al, be") V=function('V')(x, y)# A) either A or B should be uncomment

# V= x^al*y^be# B)

V_x = diff(V, x) V_y = diff(V, y)

# Differential

dV = V_x * dx + V_y * dy show(dV)

# Dérivée du premier ordre
sol=solve(dV==0, dy)
show(sol/dx)
# Dérivée du second ordre
y_x=sol.rhs()/dx
show(y_x)
hh=y_x.function(x,y)
y=function('y')(x)
hh_x=diff(hh(x,y),x).full_simplify().subs(diff(y(x), x)==y_x).full_simplify()
show(hh)
show(hh_x)


$\frac{\mathit{dy}}{\mathit{dx}} = -\frac{\frac{\partial}{\partial x}V\left(x, y\right)}{\frac{\partial}{\partial y}V\left(x, y\right)}$

$-\frac{\frac{\partial}{\partial x}V\left(x, y\right)}{\frac{\partial}{\partial y}V\left(x, y\right)}$

Now I will work on the substitution of the chosen function. And when I will have found I will come back.

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