Solve $F\left(x\,y\right)\=0$ for $y_{\+}\left(x\right)$ 

$x^2\+y^2-9\=0$

$\stackrel{\text{solutions for y}}{\to }$

$\sqrt{9-x^2}\,-\sqrt{9-x^2}$

$\stackrel{\text{select entry 1}}{\to }$

Show that $F\left(x\,y_{\+}\left(x\right)\right)\=0$ is an identity

$\genfrac{}{}{0ex}{}{}{\phantom{x\=a}}|\genfrac{}{}{0ex}{}{\phantom{\mathrm{f(x)}}}{y\=}$

$0\=0$

The Context Menu option "Label" is used to select "Label Reference" so that the item referenced by the equation label is visible, not just the equation label.

Differentiate $y_{\+}\left(x\right)$ 

$\frac{\ⅆ}{\ⅆ x}$ = $-\frac{x}{\sqrt{9-x^2}}$$$