# Exact Differential

#### ssh

##### New member
Q. Show that f(z)dz defined in a region is exact if and only if f(z) has a primitive.

#### chisigma

##### Well-known member
Re: exact differential

Q. Show that f(z)dz defined in a region is exact if and only if f(z) has a primitive.
Usually thye concept of 'exact differential' refers to a multivariable function. In case of two variables x and y, an expression like...

$\displaystyle A(x.y)\ dx + B(x,y)\ dy\ (1)$

... where A(*,*) and B(*,*) are defined in a field D, is called exact differential if it exist an F(x,y) differentiable in D for which is...

$\displaystyle dF = A(x,y)\ dx + B(x,y)\ dy\ (2)$

The expression (1) is an exact differential if and only if $A(x,y)$, $B(x,y)$, $\displaystyle \frac{\partial A}{\partial y}$ and $\displaystyle \frac{\partial B}{\partial x}$ are continuos and is...

$\displaystyle \frac{\partial A}{\partial y}= \frac{\partial B}{\partial x}\ (3)$

Kind regards

$\chi$ $\sigma$