Proof of the Compound Angle Formula for sin(A-B)
The compound angle formula can be proved using simple trigonometry. Consider the right angled triangle below with internal right angled triangles constructed with internal anglesand
With sides labelledandas shown below, we can find sides in terms of x and h.
By labelling extra angles as below,
we deduce that
Equating these expressions for x gives
h now cancels from both sides to give