Question: how to calculate the square root of a negative number in excel?
Answer: First, to square a number, multiply the number by itself. ... 
The square root of 16 is 4.
Instead of using the SQRT function, you could also use an exponent of 1/2. ... 
If a number is negative, the SQRT function returns the #NUM! ... 
You can use the ABS function to remove the minus sign (-) from a negative number.