Answer:
[tex] \cos \bigg( \frac{7\pi}{12} \bigg)= \frac{1 - \sqrt{3} }{2 \sqrt{2} } [/tex]
Step-by-step explanation:
[tex] \cos \bigg( \frac{7\pi}{12} \bigg) \\ \\ = \cos \bigg( \frac{7 \times 180 \degree}{12} \bigg)\\ \\ = \cos \bigg( {7 \times 15 \degree} \bigg)\\ \\ = \cos \bigg( {105 \degree} \bigg)\\ \\ = \cos \bigg( {60\degree + 45 \degree} \bigg) \\ \\ = \cos {60\degree .\cos 45 \degree} - \sin {60\degree .\sin 45 \degree} \\ \\ = \frac{1}{2} . \frac{1}{ \sqrt{2} } - \frac{ \sqrt{3} }{2} .\frac{1}{ \sqrt{2} } \\ \\ = \frac{1}{2 \sqrt{2} } - \frac{ \sqrt{3} }{2 \sqrt{2} } \\ \\ \huge \purple{ \boxed{ \cos \Bigg( \frac{7\pi}{12} \Bigg)= \frac{1 - \sqrt{3} }{2 \sqrt{2} } }}[/tex]
