It's because it's 9^(3/2). When powers are expressed in fractions, that means that the denominator of the fraction is the root, and the numerator is what the base is actually raised to.
9^(3/2) becomes â9^(3). (The square root of 9 raised to the third power.)
â9^(3)
â729
27
Try putting it into your calculator. =] Make sure you put parenthesis around the 3 if you're using the caret.