[tex]3( \cos {}^{2} ( \frac{\pi}{12} ) - \sin {}^{2} ( \frac{\pi}{12} ) ) = 3 \times \cos( \frac{2\pi}{12} ) = \\ 3 \times \cos( \frac{\pi}{6} ) = 3 \times \frac{ \sqrt{3} }{2} = \frac{3 \sqrt{3} }{2} [/tex]