So Sine and Cosine are related? (or...have you ever seen the rain?)

Dynamic geometry can help show relationships that printed textbooks can only hint at.  If all you saw in this was that the getting from the cosine graph to the sine graph all you had to do was "shove" it to the right a bit, you'd be well on your way.

For the more utilitarian, here is a more well known device.

For more, see www.davemath.com