If the hypotenuse (r) is also the radius of a circle,
point P moves along the circumference as the angle
changes in size. As angle θ increases, side y increases
in length while the length of the hypotenuse (or radius)
remains the same. Therefore, the value of the sine
increases as the angle increases. Changes in the value
of the sine corresponding to changes in the size of the
angle are shown on the sine curve shown in figure 12-2.
On the sine curve, the size of the angle is plotted
horizontally and the value of the sine vertically