The identity of the person is not known. Some people believe that the symbol comes from the first letter of the Arabic word for root. Others believed that it comes from the letter "r" from the Latin word, radix = root.
It was first used in print by Christoff Rudolff in 1525 in Die Coss.
The radical symbol for square root, without the vinculum above the radicand, was introduced in 1525. The first author to use it was Christoff Rudolff.
If unspecified, the square root is the principal root, which is the positive root.
It is the RADICAL SIGN , its definition is - the symbol used to indicate a nonnegitive square root.
Actually a negative number can be under a square root symbol. This becomes very useful in electrical calculations. The square root of -1 is j. That is, j2 = -1.
The radicand.