Trig Equation from JEE Mains 2016 P1 Q. 39

From a channel Lumen includes in full: Essentials of Math posts a full abstract algebra lecture series plus carefully worked olympiad and contest geometry problems, with complete proofs.

A 6-minute video from Essentials Of Math's catalogue; the title names its topic.

Video by Essentials Of Math, played through YouTube's embedded player.