- #1

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## Homework Statement

## Homework Equations

[tex]\frac{\delta{F}}{\delta{y}} - \frac{d}{dx}\frac{\delta{F}}{\delta{y'}} = 0[/tex]

## The Attempt at a Solution

I'm having trouble setting this one up. If I let the functional be

[tex]F(x,x',y) = n(y)\sqrt{1+(x')^2}[/tex]

Applying the LE equation I obtain:

[tex]\frac{d}{dy}\frac{x'}{\sqrt{1+(x')^2}}n_0(1-\frac{y^2}{a^2})=0[/tex]

And this is where I stopped (I haven't used either of the hints). Any hints?