The Tangent Line Problem

y =

2

x

-x



h

How do you find the slope of the tangent line to a function at a point Q when you only have that one point? This Demonstration shows that a secant line can be used to approximate the tangent line. The secant line PQ connects the point of tangency to another point P on the graph of the function. As the distance

h

between the two points decreases, the secant line becomes closer to the tangent line.