I am completely lost on this one:

Tutor.com | Session Transcript - Math - Calculus, 11/15/2009 7:46PMIn the engine below a 7 inch connecting rod is fastened to a crank of radius 3 inches. The crankshaft rotates counterclockwise at a constant rate of 200 revolutions per minute. Find the velocity of the piston when theta= pi/3. You will need to use the law of cosines.

I don't really even get how to draw this as a triangle - PLEASE HELP!!