de Moivre's theorem and roots of polynomials - teaching notes and examples

This worksheet can be used to introduce de Moivre's theorem to your class and show how it can be used to find multiple angle formulae (e.g. sin 4theta = ...) and how these formulae help us to relate trigonometric equations to polynomial equations.

The introduction shows how we can arrive at 2 different results for (c + is)^n by using de Moivre's theorem and a binomial expansion. There are then 3 examples of using this technique to derive multiple angle formulae.

The second section focuses on relating trigonometric equations to polynomial equations and how this allows us to find exact values of trigonometric functions or to express the roots of a polynomial in trigonometric form. There are 3 examples to illustrate this, the first one is deliberately straightforward to help students see the connection between the trigonometric work and the polynomial equation.

The solutions version of the worksheet has fully-worked solutions to all the examples and the notes in the introduction section are also completed.

Once you have worked through this worksheet with your students they should be able to attempt an exercise of questions on their own.