\sqrt[root]{arg}
The \sqrt
command produces the square root (radical) symbol with the
argument as radicand. The
optional argument, root, determines what root to produce, i.e. the
cube root of x+y would be typed as $\sqrt[3]{x+y}$
.
The radical sign is variable size, that is, it is made larger if the radicand is, for example, a built-up fraction.