Just move your mouse! The radius and angle will change to fit with the mouse's position, and as a result changing the lengths of sine, cosine tangent. Press space to see three more - secant, cosecant and cotangent. They will replace the old ones, press space again to make them come back. It might look like secant is just a random line, but it actually ends where the tangent would cross the x-axis. Click space and you will see that the green tangent line ends at the same place. In other words, it completes the triangle: radius-tangent-secant.
