Question

Express the following as a function of a single angle? Cos^2(81 deg) - sin^2(81 deg)

Answer 1

`cos(162˚)`

Explanation:

Recall that

`cos^2x - sin^2x= cos(2x)`

Then

`cos^2(81˚) - sin^2(81˚) = cos(2 * 81˚) = cos(162˚)`

Hopefully this helps!