We have:
[tex]\cos (\frac{\pi}{6})=\frac{\sqrt[]{3}}{2}[/tex]
And
[tex]\cos (\frac{\pi}{3})=\frac{1}{2}[/tex]
After that, we proceed as follows:
[tex]\sin (\frac{\pi}{3})=\frac{x\sqrt[]{3}}{2x}\Rightarrow\sin (\frac{\pi}{3})=\frac{\sqrt[]{3}}{2}[/tex][tex]\cos (\frac{\pi}{3})=\frac{x}{2x}\Rightarrow\cos (\frac{\pi}{3})=\frac{1}{2}[/tex][tex]undefined[/tex]
