The trigonometric equation is
.
Quotient identity :
.

Apply cosine half-angle identity :
.

Solve
.

The general solution of
is
, where
is an integer.
The solution is
, where
is an integer.
Now find the solutions on the interval
.
If
,
.
If
,
.
Thus, the solutions are
and
on the interval
.
The solutions of
are
and
on the interval
.