The square root of a negative number is an imaginary number. Imaginary numbers are not, by themselves, useful solutions to math problems; but they can be used to find them.
ANNA: Well, that's like 3 squares of 100 square meters. The square root of 100 is 10, so the rectangle is 10 by 30.
The logarithm of a square root is one half the log of the number itself; hence, the natural log of 25 is 3.2189, while the natural log of 5 is 1.6094.