# Partial differentiation

1. Feb 19, 2006

### Isma

i ve never read partial DE...nd i dont kno how to do this question i got in homework...plzz help
(x^2+y^2+z^2)^-1/2=V
prove dv^2/dx^2 + dv^2/dy^2 + dv^2/dz^2 = 0
(i wrote "d" for partial differential)
i know its a basic question but i cant understand the technique

2. Feb 19, 2006

### HallsofIvy

What course is this for?
It doesn't matter that you have "never read partial DE"- this problem has nothing to do with differential equations. It has to do with taking the derivative. If you mean you have not done partial derivatives, the derivative of V with respect to x is just the ordinary derivative, treating y and z as constants. Similarly, the derivative of V with respect to y is just the ordinary derivative, treating x and z as constants; the derivative of V with respect to z is just the ordinary derivative, treating x and y as constants.

Find the second derivative of V with respect to each variable, and add them!

3. Feb 20, 2006

### Isma

thx....that was easy
it is for Calculus 2 course