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Angle x is a third quadrant angle such that cosx=−1/5 .

What is the exact value of cos(x/2) ?

 Apr 1, 2020
edited by ocmaz  Apr 1, 2020
 #1
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Please re-format your question so it is correct....  is that SUPPOSED to be   - 1/5

                                                                               is that SUPPOSED to be cos (2x)   or  cos (x/2) or cos^2 x ?

 

 

I think this is the trig identity you may need:

 

 

If angle x is in Q III...then x/2 will be in Q I    and will be + POSITIVE    in value   

 Apr 1, 2020
edited by ElectricPavlov  Apr 1, 2020

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