Spesh 1/2 Unit circles

[Buoyancy]

Hi guys I need help for question 3c, I'm having trouble trying to find out the values for theta, the way I did it for this question was to find the value of root3/2 then add or subtract pie until i reach the restricted domain. Tbh I don't really know how it works, I'm a bit confused; may someone please help me?

Thank you very much!

[TheAspiringDoc]

I find it's really helpful to learn the unit circle values in degrees, radians, and cos and sin values. Then you can just link the cos value (sqrt(3)/2 in your case) to the rotation on the unit circle (that cos value corresponds to 60 degrees and/or 330 degrees, which we express as Pi/3 and 11pi/12, respectively.).
Since the value of theta is actually tripled before taking its cosine, just calculate one third of the values I've provided above. This gives:
Theta = Pi/9 or 11pi/36
I hope I've told you the right thing (check your textbook answers haha!)

[Buoyancy]

Thank you doc!