Question

What is a double angle formulae?

Answer 1

I know it can be derived from the sum/difference formulae

Answer 2

Please your own answer, not wikipedia stuff

Answer 3

\[\sin(\theta \pm \phi) = \sin \theta \cos \phi \pm \sin \phi \cos \theta \]\[\cos( \theta \pm \phi) = \cos \theta \cos \phi \mp \sin \theta \sin \phi\]\[\tan( \theta \pm \phi) = {\tan \theta \pm \tan \phi \over 1 \mp \tan \theta \tan \phi}\]

Answer 4

well the standard forms are

sin(2x) = 2sin(x)cos(x)

cos(2x) = cos^2(x) - sin^2(x)
= 2 cos^2(x) - 1
= 1 - 2sin^2(x)
tan(2x) = 2tan(x)/(1 - tan^2(x))

these can all be derived from the sum of 2 angles for each ratio

Answer 5

How would you simplify this?
sinTheta cos theta /tan theta