Question

Help me please and thanks.

Answer 1

Below

Explanation:

Use trig identity :

cos (x/2) = +- sqrt ((1+cos x)/2) = +- sqrt((1 + -2/3)/2)

= +- sqrt (1/3 /2) = +- sqrt (1/6)

since x is in Q II , x/2 is in Q I (where cos is positive ) the positive value is the one you need: sqrt (1/6 ) ( or sqrt (6) / 6 )