Formulas
There are some common formulas you should know. The first is about tangent and its relationship to the sine and cosine functions. We can derive the formula in the following way:
This leads us to this:
The next one we get from studying the graphs of sine and cosine as function θ over time. Here are those graphs:
Figure 12.9 – The graphs of sine and cosine [8]
You may notice that they are "out of phase" by π/2. This leads us to the next formula:
While I will not derive it, the following is called the Pythagorean identity, and you should commit it to memory:
