CPM Homework Help : CCA2 Problem 12-131

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12-131.

Write each angle as the sum or difference of two special angles and then find the exact sine or cosine.

$\sin\frac{7\pi}{12}$
Step 1(a):
What two special angles have a sum of $\frac { 7 \pi } { 12 }$ ? $\sin\left(\frac{\pi}{3}+\frac{\pi}{4}\right)$
Step 2(a):
Now find the exact value of sine.
Answer (a):
$\sin\left(\frac{\pi}{3}+\frac{\pi}{4}\right)\ =\ \frac{\sqrt{6}+\sqrt{2}}{4}$

$\cos\frac{11\pi}{12}$
Hint (b):
Use the same method as part (a).

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