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The implicit function:

$$\Phi(x,y) = \sqrt{x^2+1} + \sqrt{y^2+1} + 7$$

...is a solution to which of the following exact differential equations?

$\frac{x}{\sqrt{x^2+1}} + \frac{y}{\sqrt{y^2+1}} \frac{dy}{dx} = 7$

$\frac{y}{\sqrt{y^2+1}} + \frac{x}{\sqrt{x^2+1}} \frac{dy}{dx} = 0$

$\frac{x}{\sqrt{x^2+1}} = \frac{y}{\sqrt{y^2+1}} \frac{dy}{dx}$

$\frac{x}{\sqrt{x^2+1}} = - \frac{y}{\sqrt{y^2+1}} \frac{dy}{dx}$

None of the Above