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Angle x is a third quadrant angle such that cosx= −2/5. What is the exact value of cos(x/2)?

 

cos(x/2)=

 Mar 10, 2020
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Trig identity    cos(x/2) = sqrt (  (1+cosx)/2 ))  =  sqrt (( 1-2/5)/2)  = sqrt (3/10)   = sqrt 30  / 10

 Mar 10, 2020

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