Everyone knows the obvious trig identities like sin^2 + cos^2 =1, cosx=1+ sin^2, and tanx =sin/cos. I ran across an old identity the other day: 3cos^2(3x)+3sin^2(3x)=3. Can anyone here figure out why and how? I tried it and couldn't figure it out.
The calculus book places an emphasis on multiple powers of trig functions in the book. Does anyone here really know what the integral of sin^2dx is? What about the integral of cos^2dx is? I don't think I ve actually ever seen it.