Question

prove that sin theta - 2 sin ^3 theta/2 cos^3 theta - cos theta​

Answer 1

$\frac{sina - 2 {sin}^{3} a}{2 {cos}^{3} a - cosa} \\ \\ = \frac{sina(1 - 2 {sin}^{2} a)}{cosa(2 {cos}^{2}a - 1) } \\ \\ = \frac{sina(cos2a)}{cosa(cos2a)} \\ \\ = \frac{sina}{cosa} \\ \\ = tana$