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## Homework Statement

if

[tex]f \left( x,y \right) =xy*g \left( 7\,{x}^{2}-9\,{y}^{2} \right)[/tex]

then the differential equation [tex]9y\frac{{\partial f}}{{\partial x}} + 7x\frac{{\partial f}}{{\partial y}} = ?[/tex] is equal to?

## Homework Equations

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## The Attempt at a Solution

i triedto do a partial derivatives which doesn't really seem to work

if you can just give me a direction in which to go to

thanks