Sarah came into the kitchen, followed by the family dog, a black lab named Coal. The screen door banged three times behind her. Both the dog and the human looked exhausted. Sweat dripped off Sarah's reddened face; Coal panted noisily. "It sure is great to be able to get outside and work off the tension of those exams. Did you know that the Carters have a new dog, some sort of shepherd? She and Coal spent 10 minutes sniffing. Thought I never would get started on my run."
No answer came from her mother who was back at the breakfast
table staring at Sarah's computer. Her mother was an elementary school
teacher, but school was out, and she had plunged into her newest study
full time. "How's
it going?" Sarah inquired.
"I think I understand rates of change. But what is a derivative?"
"That's an instantaneous rate of change."
Her mother looked uncertain.
"Explain it to me in terms of the graph. There seems to be a graphing tool available with this program. How can I use it to understand instantaneous rates of change?"
Sarah grabbed a dish towel to wipe her face and slumped into a chair. Her mother said absently, "Don't use the dish towels, Dear." But it was just a reflex, not a real concern. Sarah ignored it and explained to her mother how to use the zooming feature of the graphing tool.