You cannot take the square root of a negative number and get a real number answer. You can only get an imaginary root.
square root of 49 = 7 and square root of 64 = 8
square root of 61 is between 7 and 8.
It would be closer to 8.
square root of -49 = 7i and square root of -64 = 8i
square root of -61 would be closer to 8i