How do you proceed i dont get how they got 5pi/12 as thetha

How do you proceed i dont get how they got 5pi/12 as thetha 112 MATHEMATICS
Squaring and adding, we obtain
_ us-I
2
2
6-1
(6)2+1
4
sine =
4
Hence, r which gives
cosO =
Therefore, 0 = — + _ =
— (Why?)
4 6 12
Hence, the polar form is
57t
cos—+isin—
12
12
- Miscellaneous Exercise on Chapter 5