i entered $\displaystyle cos (\frac{\pi}{6})$ in my calculator and the answer was $\displaystyle 0.8660254038$. the book's answer is $\displaystyle \frac{\sqrt{3}}{2}$.

i also did >Frac on my calc and it just showed the decimal form again, not the fraction form. is there a way to transform the decimal answer into the fraction answer?