​Trig help! I really don’t understand how you do this.

2. The cos is  > 0   from  [0, to pi/2)   and from (3pi/2,  2pi ]

    The csc  is < 0  where the sine is < 0....from  (pi, 2pi )

So the cos > 0  and csc < 0   from  (3pi/ 2, 2pi )

3.  cos (theta)  = - sqrt (3) / 2       at    -5pi/ 6   and at  7pi/ 6