Test nr 1
[tex]2. \: a) \: sin {15}^{°} = sin( {45}^{°} - {30}^{°}) = sin( {45}^{°}) \times cos( {30}^{°}) - cos( {45}^{°}) \times sin( {30}^{°}) = \frac{ \sqrt{2} }{2} + \frac{ \sqrt{3} }{2} - \frac{ \sqrt{2} }{2} \times \frac{1}{2} = \frac{ \sqrt{6} }{4} - \frac{ \sqrt{2} }{2} = \frac{ \sqrt{6} - \sqrt{2} }{4} [/tex]
[tex]2. \: b) \: cos {75}^{°} = cos( {30}^{°} + {45}^{°}) = cos( {30}^{°}) \times cos( {45}^{°}) - sin( {30}^{°}) \times sin( {45}^{°}) = \frac{ \sqrt{3} }{2} + \frac{ \sqrt{2} }{2} - \frac{ {1} }{2} \times \frac{ \sqrt{2} }{2} = \frac{ \sqrt{6} }{4} - \frac{ \sqrt{2} }{4} = \frac{ \sqrt{6} - \sqrt{2} }{4} [/tex]
[tex]3) \: 1) \: cos \frac{4\pi}{5} \\ 2) cos \frac{5\pi}{6} \\ 3)cos \frac{6\pi}{7} [/tex]
