Texas Instruments TI-83 Plus Manual Book page 92

Example 3–Examine the relationship between the slope of a
secant line on a curve and a tangent line to the curve.
f
Secant line
Tangent line
2
What is the slope of the tangent line of f(x) = x at x = 3?
Compare the slope of the secant line to the tangent line as the
point (x+h,f(x+h)) gets closer to the point (x,f(x)) at x = 3. The
derivative of the function at x = 3 is the slope of the tangent line.
TI-83 Plus CellSheet™ Application Page 92