This self checking worksheet was one of the original worksheets I made. My Algebra 3 students were trying to grasp the concept of using a Trig formula when they asked for a worksheet. One of my students mentioned how much better the homework would be if it was funny, too. So I started making self checking worksheets for my students. They much prefer them to odd problems in the book. This particular worksheet works with Sum-to-Product formulas. Most of them have values which will cancel either with a zero or positive/negative combination. The riddle at the bottom is one of my favorite position riddles.