Derivative

Jennifer pointed to the cartesian plane again. "You see the center of this grid?" she asked the class. "This is the foundation of Calculus."

Out in the lecture hall, one student raised a hand.

"Yes?"

"So then when do we get to learn how to prevent tartar build up?"

"Are you sure you're in the right class?"

"This isn't a seminar for dental hygienists?"

"No, this is an advanced math class."

The girl mumbled something about getting a refund from the tuition office as she sauntered out. At least that explained why she had been the only one wearing scrubs.