Type the equation $a\=\dots$

Context Panel: Assign Name

Context Panel: Evaluate and Display Inline

Context Panel: Evaluate and Display Inline

Expression palette: square-root template

Context Panel: Evaluate and Display Inline

To unassign the name $a$ interactively, use the Variables palette. (See Table A-1.2.)

Assign to the name a.

$a≔\frac{22.0}{79}\+\frac{34}{23}$

Use the sqrt command for $\sqrt{a}$.

$a^2\,\frac{1}{a}\,\mathrm{sqrt}\left(a\right)$

Remove the assignment to a with the unassign command.
Quotes are essential.

$\mathrm{unassign}\left(\'a\'\right)$