Vertical Spacing
Some formulas such as $\overline a+\overline b=\overline {a\cdot b}$, $\sqrt{a}-\sqrt{b}$, do not look quite right when it comes to vertical spacing. Fortunately, there is more than one way to fix this. One can for instance employ the \mathstrut
command as follows:
$\sqrt{\mathstrut a} - \sqrt{\mathstrut b}$
Which yields: $\sqrt{\mathstrut a} - \sqrt{\mathstrut b}$. Or using \vphantom
(vertical phantom) command, which measures the height of its argument and places a math strut of that height into the formula.
$\sqrt{\vphantom{b} a} - \sqrt{b}$
Which renders as: $\sqrt{\vphantom{b} a} - \sqrt{b}$.
Another issue is with the spacing within lines in situations like this,
Based on the previous technique, we can simplify $\dfrac{1}{\sqrt{\vphantom{b} a} - \sqrt{b}}$, and we thus get the result of the previous limit. [this text is added to show alignment with the above smashed object]
These two lines are too far apart, but this is unnecessary since the second line is very short. We can solve this by using the \smash
command, to get:
Based on the previous technique, we can simplify $\smash{\dfrac{1}{\sqrt{\vphantom{b} a} - \sqrt{b}}}$, and we thus get the result of the previous limit. [this text is added to show alignment with the above smashed object]
Beware - as above - the smashed text may overlap the next line if that line extends far enough to reach the smashed object, so this solution is not always feasible (it is esp. likely to occur in slim-width browsers, e.g. phones). Analogous overlapping may occur with any prior lines. Note that smash can be restricted to top or bottom with an argument: \smash[t]...
or \smash[b]...