From Förberedande kurs i matematik 2

If we write \displaystyle \sqrt{x} in power form \displaystyle x^{1/2}, we see that the square root is a function having the appearance of \displaystyle x^n and its derivative is therefore equal to

\displaystyle f^{\,\prime}(x) = \frac{d}{dx}\,\sqrt{x} = \frac{d}{dx}\,x^{1/2} = \tfrac{1}{2}x^{1/2-1} = \tfrac{1}{2}x^{-1/2}\,\textrm{.}

The answer can also be written as

\displaystyle f^{\,\prime}(x) = \frac{1}{2\sqrt{x}}

since \displaystyle x^{-1/2} = \bigl(x^{1/2}\bigr)^{-1} = \bigl(\sqrt{x}\,\bigr)^{-1} = \frac{1}{\sqrt{x}}\,.