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February 14th, 2012, 12:25 AM   #1
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Unit circle problem!

With the help of the unit circle, decide the exact value off:

cos?(90+v)+2cos?(180+v)


(Thx for any help!)
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February 14th, 2012, 12:48 AM   #2
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Re: Unit circle problem!

Use the angle sum identity for cosine to state:





Since:









We have:





From the diagram, we see:

and so we now have:



Another way to proceed would be to graphically add 90 to v and we the x-coordinate is -0.8. Then graphically add 180 to v and doubling the x-coordinate we get -1.2, and their sum is -2.
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