Another Proof Without Words

So the first proof without words lesson went so well that I devised a follow-up. The original proof is from Proof Without Words by Roger Nelsen. In some ways I like this one even more because my students often find the initial statement with the inverse trig functions to be completely baffling. It is also nice because it makes the kids dig out some of their geometry skills to justify the necessary angle measurements. Here is the Pages '09 File: The Proof Is In The Diagram 2.pages