BBC
Bbc: Differentiations
This site presents a tutorial on the topic of differentiation. Points of focus include rules for differentiation, tangents to curves, derivatives, increasing and decreasing functions, and optimization. Examples and a practice test are...
Wikimedia
Wikipedia: Gottfried Leibniz
Wikipedia offers detailed biographical information on Gottfried Leibniz (1646-1716 CE), who coined the mathematical term, "Function."