What is the square root of negative one?

What is the square root of negative one?

A square root is a number that when multiplied by itself is equal to a given number, any number times itself must be positive, not negative... there is no square root of a negative real number, but you could use a complex number, which is in form a + bi, bi is an imaginary number...
I = sqare root of 1, so I squared = 1

e.g. square root of -16 = square root of (-1) x 16 = I x 16 = 4i