U.T. ARLINGTON CALCULUS I       LAB I.2 (Last revision June 2004.)
Objective
To understand the derivative function of sinx and the derivative function of ex.
Procedure
Answer the questions below on a sheet of paper unless otherwise instructed. Write your answers as completely and neatly as possible. Put your name at the top right of the paper and put the title ``Calculus I   Lab I.2'' at the top center.
Due-date
Your instructor should tell you if any of this lab is to be turned in for grading and what the due-date is.  If not, then ask.

Introduction
The derivative of a differentiable function f at x = a is the slope of the tangent line to the graph of f at the point ( a, f(a) ) and is given by
which is the limit of the slopes of secant lines passing through (a, f(a)). In this lab, call this limit g(a).

## PART A

Step 1
Suppose f(x) = sinx where x is in radians. Our goal is to guess the function g, which is the derivative function of sinx.

You are going to use a browser to access a certain site given below. For this to work properly, java needs to be "allowed" or "on" in the preferences. You will alternate between that site and this one, so you might want to call up a new browser window, so that you can jump between that site and this one and look at them both at once. I recommend that you copy and paste the site's address into the new browser window rather than clicking on it.

You should eventually (!) get a page with an xy-coordinate system and instructions. Once you get to that site, read the instructions there (they are below the coordinate system) and apply those instructions to the function sinx. Estimate the slope of sinx at the values of a (or, as close as possible to the values of a) given in the following table. Record your data and be careful to notice if the slope is negative (it is difficult to see the negative sign on the screen!   :-(     ).

Go to http://www.uta.edu/math/Calculus/secant.html.

### Question A1.

Table: Slope for f(x) = sinx
 a -3/ 2 -5 / 4 - -3 / 4 - / 2 - / 4 0 / 4 / 2 3 / 4 5 / 4 3 / 2 g(a) = slope of f at a
Step 2
We will now get Mathematica to plot these points for us on a graph. To do this, highlight and copy the commands located at http://www.uta.edu/math/Calculus/sine.html by using the ``Edit'' menu. Do NOT exit the browser. Call up Mathematica (double-click on its icon or use ``program'' menu under ``start'' menu) and paste (using the ``Edit'' menu) into the untitled window. The commands pasted have the above x-coordinates without their corresponding y-coordinates. Notice that Mathematica uses "Pi" for . Edit the commands by entering the corresponding y-coordinates (your estimates in your table) where the ``?'' are, and then enter your commands by pressing the ``Enter'' key at the South East corner of the keyboard. (If you have trouble with the ``Enter'' key, try "Shift" and "Enter" together.) You should get a graph of your table of data. Sketch the graph on your sheet of paper (do NOT print yet).

### Question A2.

Which trigonometric function best describes your graph?
This function is the derivative of sinx.

## PART B

Step 1
Repeat Step 1 in PART A for the function f(x) = ex so that you may fill in the table below.

### Question B1.

Table: Slope for f(x) = ex
 a -3 -2 -1 0 1 2 3 4 5 5.5 6 g(a) = slope of f at a
Step 2
Repeat Step 2 in PART A for this table of data using the commands at http://www.uta.edu/math/Calculus/exp.html. This time print out your graph. (To print: highlight the bracket on the far right of the window level with your graph; then go to the ``file'' menu and select ``print selection''. Your graph should print on the printer in the pc lab. )

### Question B2.

Which exponential function best describes your graph?
This function is the derivative of ex.

### Question B3.

• How are the function ex and the function you found for the derivative of ex related?
• If c is a constant real number, how are the function cex and the function obtained by differentiating cex related?

### Note

Labs I.3 & I.4 will repeat this lab for the functions 2 x, 3 x, b x and lnx.

END LAB I.2
Save any work you wish to save to a disk.
Exit the browser and Mathematica.