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

Enter your answer, in simplest radical form, in the box.

cos (x/2) = ___

 Aug 21, 2021
 #1
avatar+118609 
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More information please.

 Aug 21, 2021
 #2
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sorry it says 

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

what is the exact value of cos(x/2)

enter your answer in the simpliest radical form 

Guest Aug 21, 2021
 #3
avatar+33615 
+2

Use the fact that \(cos(x)=2cos^2(x/2)-1\)

 Aug 21, 2021

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