A complex number is a number of the form a+bi,
if b=0, that is if the number is a, then it is a Real number
if a=0, that is if the number is bi, then it is called an imaginary number.
All imaginary numbers are complex numbers.
Also, all real numbers (non-imaginary) are complex numbers.
Thus, all the numbers given are complex.
3i : imaginary
-5i : imaginary
6-i: complex
square root of 21: real, non-imaginary, complex
Negative square root of 16=-4: real, non-imaginary, complex
Square root of -14 = (square root of 14)i: imaginary
