Explanation of 12.3.37

Problem number 37 is the question about the ball drop, which I did the hard way until I looked back at the chapter. You do the exact same calculation that you would for a normal geometric series, with a1(1-r^k)/(1-r), except that you have to add the initial drop distance, and calculate a1. If an represents the distance from the ground, up, and back to the ground again, then a1 would be 8, because you go up 4 feet and then fall down 4 feet.