<PRE><B>Question 172974</B>
I will do number 3 and leave the rest to others.

3.  Find the exact value of: cos315 degrees.


Cos315 lies in quadrant 4.

We need to find its reference angle.

To do so, subtract 315 degrees from 360 degrees.

Then:

360 degrees - 315 degrees = 45 degrees

The cosine of an angle is positive in quadrant 4.

The exact value of cos315 = cos45 = sqrt{2}/2

Final answer: sqrt{2}/2

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