There was a real problem in the 1600's trying to determine how to mathematically represent instantaneousness. If a tangent line of a curve at a particular point can be drawn accurately enough, it's slope is the instantaneous slope of the curve at that point. In this help video, I show you how to go from secant to tangent, average to instantaneous and algebra to calculus at the magic mid time of an interval. I also show how to work example 4a and 4b.