exact value

Hello, jumpman23!

Recall the compound-angle identities:

. . $\begin{array}{ccc}\sin(A\pm B) &=&\sin A\cos B \pm \cos A\sin B \\ \\[-4mm] \cos(A \pm B) &=& \cos A\cos B \mp \sin A\sin B \\ \\[-4mm] \tan(A \pm B) &=& \dfrac{\tan A \pm \tan B}{1 \mp \tan A\tan B} \end{array}$

Quote:

Find the exact value of sine, cosine, and tangent of: . $\frac{7\pi}{12}$

Note that: . $\frac{7\pi}{12} \;=\;\frac{3\pi}{12} + \frac{4\pi}{12} \;=\;\frac{\pi}{4} + \frac{\pi}{3}$

Can you finish it now?