When we use an exponent of 1/2, it is the same as a square root. The more general rule is
[tex]\sqrt{x} = x^{1/2}[/tex]
In this case, we plug in x = 10.
The use of a fractional exponent is handy when you want to deal with things like cube roots on a calculator. This is because
[tex]\sqrt[3]{x} = x^{1/3}[/tex]
Many calculators don't have a button labeled [tex]\sqrt[3]{}[/tex] but they have the button [tex]x^y[/tex] to allow fractional exponents.
