Question

How do you simplify `cos^2((2pi)/9) - sin^2((2pi)/9)`?

Answer 1

`cos(80^o)=0.17365`, nearly

Explanation:

`cos^2A-sin^2A=cos 2A`
Here, `A = 2pi/9 radian=2X180/9 = 40^o`.
Answer is cos 2A = `cos(80^o)=0.17365`, nearly