The square root of a negative number is an imaginary number It can be expressed in the form ai where a is a real number and i = Examples: 2i, -3 4i, ( = i ) are imaginary numbers (See also number and complex number )
A complex number in which the imaginary part is not zero. Any number of the form a + bi where a and b are real numbers, i is the square root of -1, and b is not zero. If a is zero, the number is called a pure imaginary number. See also complex number