Pendulum diagram 3.13 has sine and cosine reversed

[shiffman]

and the text should probably make note of this

[shiffman]

Added:

Note, however that sin(angle) is used for the x-value and cos(angle) for the y. This is the opposite of the formula we established in Chapter 3. The reason for this is that we are looking for the top angle of the right-triangle pointing down as depicted in Figure 3.13.