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## #1 2006-03-30 09:03:24

MathsIsFun

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### Partial Differentiation Formulas

Partial Differentiation Formulas

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

## #2 2006-04-16 01:00:11

ganesh
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### Re: Partial Differentiation Formulas

If f is a function of two variables, its partial derivatives fx and fy are also function of two variables; their partial derivatives (fx)x, (fx)y, (fy)x, and (fy)y are second order partial derivatives. If z=f(x,y), then

Homogenous function :- A function f(x,y) of two independent variables x and y is said to be homogenous in x and y of degree n if
for any positive quantity t where t is independent of x and y.
For example,

Therefore, f(x,y) is a homogenous function of degree 2 in x and y.

Euler's theorem on homogenous functions
If f is a homogenous function of degree n in x and y, then

Character is who you are when no one is looking.

## #3 2006-04-16 01:09:06

Ricky
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### Re: Partial Differentiation Formulas

"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

## #4 2006-04-25 00:38:05

ganesh
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### Re: Partial Differentiation Formulas

Jacobians

If

are functions of 3 variables

then the Jacobian of the transformation from
to

is defined by the determinant

Character is who you are when no one is looking.

## #5 2006-08-06 13:05:20

Zhylliolom
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### Re: Partial Differentiation Formulas

Differential of a Multivariable Function

If z = f(x1, x2, ..., xn), then

Differentiation of Composite Functions

If z = f(x1, x2, ..., xn), where x1 = f1(r1, r2, ..., rp), ..., xn = fn(r1, r2, ..., rp), then

where k = 1, 2, ..., p.

Implicit Functions

For the implicit equation F[x, y, z(x, y)] = 0, we have

and

Surface Area

The area of a surface z = f(x, y) is given by

Theorems on Jacobians

If x and y are functions of u and v and u and v are functions of r and s, then

For 2 equations in n > 2 variables to be possibly solved for the variables xa and xb, it is necessary and sufficient that

This may be extended to m equations in n > m variables.

If u = f(x, y) and v = g(x, y), then a necessary and sufficient condition that a functional relation of the form Φ(x, y) = 0 exists between u and v is that

This may be extended to n functions of n variables.

Partial Derivatives with Jacobians

Given the equations F(x, y, u, v) = 0 and G(x, y, u, v) = 0, we have

This process may be extended to functions of more variables.

Differentiation Under the Integral Sign

If

then

Last edited by Zhylliolom (2006-08-06 13:13:30)