The final line of my attempt contains the 2 answers listed in the book, but I'm not sure what the basis for excluding all the other values under is? I have a feeling my approach is slightly incorrect here. Can anyone help me clear this up?

Many thanks.

Solve the equation for .

Q.

Attempt:. Sin is positive in the 1st & 2nd quadrants.

or

Since the angle is add & to each angle (i.e. & ):

or

or

(From text book):

Ans.