Cosine and sine of an angle θ are defined to be the x and y-coordinates of the point P on the unit circle with the property that the line from O to P makes and angle θ with the positve x-axis. cos(θ) ...

As the point P moves anticlockwise around the circle from 0°, the angle θ changes. The values of cos θ and sin θ also change. The graphs of y = sin θ and y = cos θ can be plotted.