Answer:
For theta = 0 , π , 2π , 7π/6 and 11π/6
this equation holds !!
Step-by-step explanation:
[ Refer to the attached file ]
* Cos2x = 1 - 2sin²x
* Sinx is zero for x = nπ
* Sinx is negative in 3rd and 4th quadrant !!