Hello, I'm currently trying to convert polar equations to Cartesian equations and vise-versa. I noticed an equation needed a Trig ID I am not familiar with: sin(2theta) = 2sin(theta)*cos(theta) cos(2theta) = cos^2(theta) - sin^2(theta) My apologies if that looks like an eye soar; I'm new here and don't know how to use those fancy characters. Anyway, I don't recall these ID's. I might have not been paying attention in Trig. If anyone can explain to me how they are equal I would greatly appreciate it!