Take 15 minutes to prepare this exercise.
Then, if you lack ideas to begin, look at the given clue and start searching for the solution.
A detailed solution is then proposed to you.
If you have more questions, feel to ask then on the forum.
Linearize and
Use the formulas of Euler: use then the binomial formula and regroup terms to make some sinus and cosinus appear.
We use Euler's formulas: hence
We develop the numerator with the binomial formula:
hence
