Question

How do you use the double-angle formula to rewrite the expression: `(1/3)cos^2x-(1/6)`?

Answer 1

Use the trig identity: `cos 2a = 2. cos^2 (a) - 1`.

`y = 1/3. cos^2 (x/3) - (1/6) = 1/6. (2cos^2 (x/3) - 1) = 1/6 cos ((2x)/3)`