Here is a graph of $y = \sin(x)$, x in radians. You’ve surely seen it many times. In this module, we (meaning us authors) will make sure that you understand two important things about this graph: what the values of x represent, and what the values of y represent.
Figure 2.1.1. Graph of $y=\sin(x)$
You might see the graph of $y = \sin(x)$ as just a shape. But the graph actually represents the behavior of change along a circle. To see this we must explore the meanings of y and x in the statement $y = \sin(x)$.