Plot the tangent line to the graph of the function

f(x) = ln(x - 6)

at the point x = 8 together with the graph of this function.

Using the TI-85 graphing calculator:

[Press here to see animation again!]

  1. If you are not familiar with the graphing of functions on the TI-85, then first read the Initial Setup page from Little's Basic Guide to the TI-85.
  2. Press the GRAPH key and then pick y(x)= by pressing the F1 key.
  3. If necessary, keep pressing F4 key until only y1= appears on the screen.
  4. Type in
    ln(x - 6)

    and press the ENTER key.

  5. The range settings for the graph above is  [5, 10] × [- 2, 2]:

  6. Press the MORE key so that MATH appears in the menu.
  7. Press the F1 key to choose MATH.
  8. Press the MORE key twice so that TANLN appears in the menu.
  9. Press the F3 key to choose TANLN.
  10. There is a blinking cursor on the graph at x = 7.5; using the arrow keys move this cursor along the graph so that the x value, which is indicated at the lower left hand corner of the screen is as close to 8 as possible.
  11. Press the ENTER key to draw the tangent line.