EVOLUTION, in arithmetic is the operation of finding a root of a number. The Greeks found the square root of a number by a method similar to the one given in elementary arithmetic and algebra books, and this passed on to or was independently developed by the Hindus. The latter gave rules for the cube root. Higher roots attracted the attention of various writers of the 16th century, the method being based upon the expansion of a binomial. (See BINOMIAL THEOREM.) The word "root," the Latin radix, is due to mediaeval translations from the Arabic, whence came the idea of "extracting the root," and so Recorde (fl. 1542) speaks of "pulling out" a root. The symbol for root is ./, as in V2. For roots beyond the square root the index is written, as in .I5 and 4 The symbol denotes the principal root. Every number has n nth roots, only one of which is indicated by the symbol . For example, the three cube roots of I are I, —1+1V-3, and —1-1V-3, but the principal cube root is 1.