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) =

Guest Mar 31, 2021

edited by
Guest
Mar 31, 2021

#1**+1 **

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)

ElectricPavlov Apr 1, 2021