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

 

What is the exact value of cos(x/2)?

 

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

 

cos(x/2) = 

 Mar 31, 2021
edited by Guest  Mar 31, 2021
 #1
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Trig identity       cos ( x/2)  = ±    sqrt ( ( 1 + cosx)/2)

                                         = ±  sqrt (4/10)

                                         =±  2 sqrt 10  /10

                                           = ± 1/5 sqrt 10   =  - 1/5 sqrt 10    (since original cos was in Q III    x/2 is in Q II and is negative)

 Apr 1, 2021

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