SOLUTION: what is the exact value of cos 13pi/12

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Question 237742: what is the exact value of cos 13pi/12
Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!




Notice that

From the depiction of the unit circle above it should be clear that



Now notice that

Since is known, see unit circle above, we can use the half-angle formula for cos to calculate the exact value we need.



So, knowing that , we can write:



Since is in Quadrant I,



But is in Quadrant III, so




John