Surd

In general, an unresolved nth root, commonly involving a radical symbol , is known as a surd. However, the term surd or "surd expression" (e.g., Hardy 1967, p. 25) can also be used to mean a sum of one or more irrational roots. In the mathematical literature, the term arises most commonly in the context of quadratic surds.

The term "surd" has a special meaning in the Wolfram Language, where the principal root of a complex number can be found as z^(1/n) or equivalently Power[z, 1/n]. However, when is real and only real roots are of interest, the command Surd[x, n] can be used. It returns the real-valued nth root when is real and is odd, and the principal root when is a nonnegative real number and is even.