difficult question

["tamiry"]

Hi,
Can any one please help with this:

Prove that the F(x,y) = C can be expressed as h(x,y) = C', where h is
harmonic function,
iff (@^2F/@x^2 + @^2F/@y^2)/(((@F/@x)^2)+((@F/@x)^2)) is a function of
F

F, h are real functions.
C, C' - constants.
@ - partial derivative.
@^2F/@x^2 - second order partial derivative of F by respect to x.