Simple Trigonometric Equations

These are hard for me right now, it will be fine once I understand it but I'm not sure because it's very confusing!

If I had cos 3x = 0.5, would I:

Use cos^-1 0.5 = 60

and because cos is positive in the second quadrant, would I add the 60 to 90 to make 150...

then divide both answers by 3 to get 20 and 50?

Is this right, and would it work for any other including sin?

Also if I had tan x = -root 3, would I solve it like:

tan^-1 root 3 = 60

and because tan is positive in the third quadrant, would I add the 60 again to 180 to make 240

and are my solutions 60 and 240, and nothing else?