cos(θ) is the x-coordinate of the point P and, sin(θ) is the y-coordinate of the point P. This applet shows how the graphs of sin(θ) and cos(θ) follow directly from the definition of these functions.

As the point P moves anticlockwise round the circle, the values of \(\cos{\theta}\) and \(\sin{\theta}\) change, therefore the value of \(\tan{\theta}\) will change. The graph has a period of 180°.