The trigonometric equation is
.

Quotient identity :
.

Apply zero product property.
\
or 
or
.
Solve
.

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

The general solution of
is
, where
is an integer.
The solution is
, where
is an integer.
Find the solutions on the interval
.
If
,
.
If
,
.
Thus, the solutions are
and
on the interval
.
Therefore, the solutions of
are
,
,
,
, and
on the interval
.
Observe the given options :
\
is not a solution of
.
Option D is the corrrect choice.
\Option D is the corrrect choice.