Thanks Heureka,
Here is another approach.
\(\sin \frac{\pi}{12} + \sin \frac{3\pi}{12} + \sin \frac{5\pi}{12} + \sin \frac{7\pi}{12} + \sin \frac{9\pi}{12} + \sin \frac{11\pi}{12}\\ =\sin \frac{\pi}{12} + \sin \frac{3\pi}{12} + \sin \frac{5\pi}{12} + \sin \frac{5\pi}{12} + \sin \frac{3\pi}{12} + \sin \frac{\pi}{12}\\ =2(\sin \frac{\pi}{12} + \sin \frac{3\pi}{12} + \sin \frac{5\pi}{12} )\\ =2(\sin \frac{\pi}{12} + \sin \frac{\pi}{4} + \cos \frac{\pi}{12} )\\ =2(\sin \frac{\pi}{12} + \cos \frac{\pi}{12} )+2\sin \frac{\pi}{4}\\ =2\sqrt{(\sin \frac{\pi}{12} + \cos \frac{\pi}{12} )^2}+ \frac{2}{\sqrt{2}}\\ =2\sqrt{(\sin^2 \frac{\pi}{12} + \cos^2 \frac{\pi}{12} +2\sin \frac{\pi}{12}\cos \frac{\pi}{12} )}+ \frac{2}{\sqrt{2}}\\ =2\sqrt{(1 +2\sin \frac{\pi}{12}\cos \frac{\pi}{12} )}+ \frac{2}{\sqrt{2}}\\ =2\sqrt{(1 +\sin \frac{\pi}{6})}+ \frac{2}{\sqrt{2}}\\ =2\sqrt{(1 +\frac{1}{2})}+ \frac{2}{\sqrt{2}}\\ =2\sqrt{(\frac{3}{2})}+ \frac{2}{\sqrt{2}}\\ =2(\frac{\sqrt3}{\sqrt2})+ \frac{2}{\sqrt{2}}\\ =\sqrt6+\sqrt2\)
LaTex
\sin \frac{\pi}{12} + \sin \frac{3\pi}{12} + \sin \frac{5\pi}{12} + \sin \frac{7\pi}{12} + \sin \frac{9\pi}{12} + \sin \frac{11\pi}{12}\\
=\sin \frac{\pi}{12} + \sin \frac{3\pi}{12} + \sin \frac{5\pi}{12} + \sin \frac{5\pi}{12} + \sin \frac{3\pi}{12} + \sin \frac{\pi}{12}\\
=2(\sin \frac{\pi}{12} + \sin \frac{3\pi}{12} + \sin \frac{5\pi}{12} )\\
=2(\sin \frac{\pi}{12} + \sin \frac{\pi}{4} + \cos \frac{\pi}{12} )\\
=2(\sin \frac{\pi}{12} + \cos \frac{\pi}{12} )+2\sin \frac{\pi}{4}\\
=2\sqrt{(\sin \frac{\pi}{12} + \cos \frac{\pi}{12} )^2}+ \frac{2}{\sqrt{2}}\\
=2\sqrt{(\sin^2 \frac{\pi}{12} + \cos^2 \frac{\pi}{12} +2\sin \frac{\pi}{12}\cos \frac{\pi}{12} )}+ \frac{2}{\sqrt{2}}\\
=2\sqrt{(1 +2\sin \frac{\pi}{12}\cos \frac{\pi}{12} )}+ \frac{2}{\sqrt{2}}\\
=2\sqrt{(1 +\sin \frac{\pi}{6})}+ \frac{2}{\sqrt{2}}\\
=2\sqrt{(1 +\frac{1}{2})}+ \frac{2}{\sqrt{2}}\\
=2\sqrt{(\frac{3}{2})}+ \frac{2}{\sqrt{2}}\\
=2(\frac{\sqrt3}{\sqrt2})+ \frac{2}{\sqrt{2}}\\
=\sqrt6+\sqrt2