Question

Expressing a.) cos(3θ), b.) sin(4θ) in terms of cos(θ) and sin(θ).

Answer 1

well as a start for the (a) use the sum of 2 angles

\[\cos(3\theta) = \cos(2\theta + \theta)\]

for (b)

use \[\sin(4 \theta) = \sin(2 \theta + 2 \theta) \]

for both questions it should be reasonably straight forward from here

Answer 2

How it goes when i use De Moivre's formula?

Answer 3

I wouldn't have thought you needed De Moivre...and thats used in complex numbers

Answer 4

sry, i forgot to mention those in my question.