Question 1142101
.


For the proof,  look into this link



&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<A HREF=https://math.stackexchange.com/questions/2298751/prove-by-induction-that-sinx-sin3x-sin-2n-1x-frac1-cos2>https://math.stackexchange.com/questions/2298751/prove-by-induction-that-sinx-sin3x-sin-2n-1x-frac1-cos2</A>


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;https://math.stackexchange.com/questions/2298751/prove-by-induction-that-sinx-sin3x-sin-2n-1x-frac1-cos2



An equivalent statement was proven there.