Question

Cos^2 pi/9 -sin^2 pi/9

Answer 1

This is actually a lot easier than it seems :-)! There is a formula in trig called the Pythagorean Theorem. This is cos^2 x + sin^2 x = 1. This means that cos^2 x means the exact same thing as 1-sin^2 x. If we plug this in, we get 1-2sin^2 pi/9. Another helpful trigonometric equation is the double angle identity. This is cos(2x)=1-2sin^2 (x). Plugging our equation from earlier in, we get cos 2pi/9.