\sqrt ¶Synopsis, one of:
\sqrt{arg}
\sqrt[root-number]{arg}
The square root, or optionally other roots, of arg. The optional
argument root-number gives the root, i.e., enter the cube root of
x+y as \sqrt[3]{x+y}.
The size of the radical grows with that of arg (as the height of
the radical grows, the angle on the leftmost part gets steeper, until
for a tall enough arg, it is vertical).
LaTeX has a separate \surd symbol for making a square root
without arg (see Math symbols).