P counterclockwise along the circumference of the circle.
The initial leg of any angle is the positive leg of the x axis. The functions of any angle are, collectively, various ratios that prevail between these coordinates. Actually, the sine of 45 is 0.70711. Graphically, the sine is indicated in figure 1-21 by the line AP, which measures 0.7 to the scale of the drawing. OC is equal to the unit radius, r.