- #1
iAlexN
- 16
- 0
Given [tex]V=xf(u)[/tex] and [tex] u = \frac{y}{x}[/tex] How do you show that:
[tex] x^2 \frac{\partial^2V}{\partial x^2} + 2xy\frac{\partial^2V}{\partial x\partial y} + y^2 \frac{\partial^2V}{\partial y^2}= 0 [/tex]
My main problem is that I am not sure how to express V in terms of a total differential, because it is a function of x and f(u). So it depends on a variable and a function, and doesn't x also depend on u and y?
[tex]dV = \frac{\partial V}{\partial x} * dx + \frac{\partial V}{\partial f(u)} * f(u) [/tex]
This total differential doesn't really help much, there must be some other way of writing it down and simplifying it?
So how should you go about solving this?
[tex] x^2 \frac{\partial^2V}{\partial x^2} + 2xy\frac{\partial^2V}{\partial x\partial y} + y^2 \frac{\partial^2V}{\partial y^2}= 0 [/tex]
My main problem is that I am not sure how to express V in terms of a total differential, because it is a function of x and f(u). So it depends on a variable and a function, and doesn't x also depend on u and y?
[tex]dV = \frac{\partial V}{\partial x} * dx + \frac{\partial V}{\partial f(u)} * f(u) [/tex]
This total differential doesn't really help much, there must be some other way of writing it down and simplifying it?
So how should you go about solving this?