- #1

- 60

- 11

- Homework Statement
- cos(nθ) = cos((n-1)θ)cos(θ) - sin((n-1)θ)sin(θ)

- Relevant Equations
- no equation given for this trig equation

See the attached image. Apostol gives cos(nθ) = cos((n-1)θ)cos(θ) - sin((n-1)θ)sin(θ), in the middle of the picture, but previous info given does not state how he got this equation.

To me it looks like he used the equation cos(x+y) = cosxcosy-sinxsiny

To me it looks like he used the equation cos(x+y) = cosxcosy-sinxsiny