The equation you wrote was:
I'm not sure if this is true. Consider the angle
The left side becomes:
The right side becomes:
- Using and , express everything in terms of sine and cosine.
- Multiply both sides by to get rid of fractions.
- Then use to express everything in terms of .
- Re-arrange as a quadratic in .
- Factorise. You should get:
Can you complete it now?