Theorems

Theorems are statements that summarize the results that are true in mathematics. Theorems are statements that have been proved true; but the emphasis in AP Calculus is not on proof. Rather, it is on what the theorems mean and how to use them.

Theorems have two parts: the “if …” clause called the hypothesis and the “then …” clause called the conclusion. Students need to know both parts. In many theorems the conclusion is some sort of formula. The students need to know this, but also need to know when they can use it (the hypothesis tells them that).

An early important theorem is the Intermediate Value Theorem (IVT). Take some time with this theorem. “Play” with it. The hypothesis requires that the function be continuous on a closed interval. Use graphs (sketches, no equation needed) to show cases where the conclusion is both true and false when the function is not continuous. Can the function take on values not between f(a) and f(b)? Can you find a case where the hypothesis is met, but the conclusion is false? (Let’s hope not!)

Consider the theorem (p\to q), its converse (q\to p), its inverse (\sim p\to \sim q) and its contrapositive (\sim q\to \sim p) by looking at graphs of each case. (For the IVT the converse and inverse are false. The contrapositive of any true theorem is also true.)

Finally, for this and for all the important theorems that you use this year, express them in words, “play” with them by making change to the hypothesis, and look at graphs. Don’t just state the theorem and expect students to understand it, remember it and use it correctly.

The next post will be about definitions, which are similar to theorems in lots of ways.

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