ABSTRACT
This chapter discusses derivatives. The chapter reminds the reader of the calculus and urges him to remember that a derivative measures the slope of a tangent line. In particular, an increasing function must have a positive derivative. It's enough to have some general, vague idea what the function looks like. Sometimes two well chosen values can tell you what a function is doing. Finally, the sign of a derivative is sometimes hinted at by the problem itself, especially if it's one of those nasty "word problems": A fungus culture grows until it fills its Petri dish, according to the law. The chapter also presents some problems with loads of mistakes, mostly of a negative nature (but a few of which are positively wrong).
