## Friday, November 11, 2016

### AP Calculus Curve Sketching Tips & Tricks

One of my favorite times of year in AP Calculus is that moment when we finally have enough mastery of derivative technique to start seeing the "why" to our last few weeks of "what."  These are some of my favorite conversations I get to have with my kids (and my kids get to have with each other) as we move into curve sketching.

Extreme Value Theorem (aka Wolf Blitzer's Celebrity Jeopardy Meltdown)
Extreme Value Theorem always seems to fall around election day in my curriculum and the the obvious connection between that and the candidate test are often staring me directly in the face. However, I've found that this analogy often only helps students remember the name of a test- not that actual idea of what it does.

My husband and I are both secretly 87 years old and we watch Wheel of Fortune and Jeopardy every night together. When I was recently reminded of Wolf Blitzer's total meltdown on Celebrity Jeopardy, I had a sudden ah-ha moment:
• There are only 3 candidates here- the people on the show. Are there people yelling the answers from their couch at home? Sure. But they aren't true candidates for winning since they aren't even in the studio. Same thing goes with the candidate test....you have to be in the interval to be eligible.
• While all candidates are eligible, it's pretty clear to see who the winner and loser was in this episode. There's an absolute maximum, an absolute minimum, and another candidate who just gets a "thank you for playing."
• It's easy to talk about ties with this analogy as well. If someone had tied Andy (most likely not Wolf), there would have been 2 winners (2 absolute maximums). The key is they would have had the same maximum value (y value) occurring for 2 different people (x value). It's an easy conversation to revisit when you are distinguishing between an extreme value and where it occurs.
Mean Value Theorem(aka the E-Z Pass Conspiracy Theory )

Rolle's Theorem (just think "Tootsie Roll")
My husband still talks about the day he learned Rolle's Theorem in BC Calc. He can't tell you anything about what it meant, but he remembers that his teacher gave them all dinner rolls. I thought about doing this and was talking at a dinner party one night about where to buy dinner rolls in bulk (because math teachers at a dinner party are notoriously cool). After resigning that I'd need to look like a crazy lady at a wholesale club the next day, someone I barely knew suggested I just buy Tootsie Rolls instead. I had another mini-epiphany:
• Roll sounds a lot like ROLLES Theorem (obvious, I know)
• Tootsie Rolls look like a horizontal tangent line if you hold them up to read them correctly. Their slope? Zero!
• The letter o is everywhere here: rOlles theorem, tOOtsie rOll. And what do o's remind us of? ZERO!
• You can even use the Tootsie Roll to demonstrate the theorem by sliding it between the tangent and the secant lines:
First Derivative Test- Let's Get Talking
The first derivative test is a pretty intuitive idea when you break it down....a maximum has to happen when slope changes from positive to negative and a minimum has to happen when slope changes from negative to positive. It's something you could talk about at a much lower level than AP Calc. However, it's something we need to be able to justify correctly at the AP level, so the more I can get my students to understand the intuition, the easier this will be for them. I used this activity this year:

I gave out cards like this to my students.

Each one has:
• The graph of a derivative on it
• A prompt to help students generate discussion
• An answer key on the back.
First, I had students work individually on their own problem to make sure they were the "experts" in it. Then, students "speed-dated" students with different problems, trying to determine intervals of increasing and decreasing on each. Then, in small groups, students were asked to identify what happens at the points where the intervals meet. We wrapped up with a whole class discussion to debrief and develop our final conjecture.

We still have a lot more to do in curve sketching, but these are just some of my favorite little tricks for introducing a collection of really fun ideas!