Find an exact value.
-$\cos 15 ^ { \circ }$
A) $\frac { \sqrt { 6 } + \sqrt { 2 } } { 4 }$
B) $\frac { - \sqrt { 6 } + 1 } { 4 }$
C) $\frac { - \sqrt { 2 } + \sqrt { 6 } } { 4 }$
D) $\frac { - \sqrt { 2 } - \sqrt { 6 } } { 4 }$

Question

Quizplus · Accepted Answer

$\cos 15^\circ = \cos(45^\circ - 30^\circ) = \cos 45^\circ \cos 30^\circ + \sin 45^\circ \sin 30^\circ = \frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} + \frac{\sqrt{2}}{2} \cdot \frac{1}{2} = \frac{\sqrt{6} + \sqrt{2}}{4}$.

Find an Exact Value cos⁡15∘\cos 15 ^ { \circ }cos15∘ A) 6+24\frac { \sqrt { 6 } + \sqrt { 2 } } { 4 }46​+2​​

Find an Exact Value $\cos 15 ^ { \circ }$ A) $\frac { \sqrt { 6 } + \sqrt { 2 } } { 4 }$