Now we need some everyday uses for the derivative. We need to tie it
into your day-to-day life, make you feel as if it has some immediacy for
you. We want to show how it can become more than just an acquaintance,
it can be a real friend. But what makes someone your friend? Well, it
helps if they do things for you. Send you cards on your birthday. Make you
a special dinner once in a while. Derivatives will not
do that kind of stuff for you. But they will do things that your other
friends can't do, things that will convince you to open your heart. For
instance, derivatives will tell you how fast you are going. Say you are driving
down the road, and you look at the speedometer, and it reads 65 mph. That
speedometer is telling you the