1.4: The Calculus
Learning Objectives
A student will be able to:
 Use linear approximations to study the limit process.
 Compute approximations for the slope of tangent lines to a graph.
 Introduce applications of differential calculus.
Introduction
In this lesson we will begin our discussion of the key concepts of calculus. They involve a couple of basic situations that we will come back to time and again throughout the book. For each of these, we will make use of some basic ideas about how we can use straight lines to help approximate functions.
Let’s start with an example of a simple function to illustrate each of the situations.
Consider the quadratic function
Suppose we magnify our picture and zoom in on the point
We note that the curve now looks very much like a straight line. If we were to overlay this view with a straight line that intersects the curve at
We can make the following observations. First, this line would appear to provide a good estimate of the value of
Tangent Line to a Graph
Continuing our discussion of the tangent line to
Yes, we need to find the slope of the line. We would be able to find the slope if we knew a second point on the line. So let’s choose a point
In particular, for
As we get closer to
Let’s make a couple of observations about this process. First, we can interpret the process graphically as finding secant lines from
Second, in examining the sequence of slopes of these secants, we are systematically observing approximate slopes of the function as point
Applications of Differential Calculus
Maximizing and Minimizing Functions
Recall from Lesson 1.3 our example of modeling the number of Food Stamp recipients. The model was found to be
We note that the function appears to attain a maximum value about an
Hence we can use calculus to model situations where we wish to maximize or minimize a particular function. This process will be particularly important for looking at situations from business and industry where polynomial functions provide accurate models.
Velocity of a Falling Object
We can use differential calculus to investigate the velocity of a falling object. Galileo found that the distance traveled by a falling object was proportional to the square of the time it has been falling:
The average velocity of a falling object from
HW Problem #10 will give you an opportunity to explore this relationship. In our discussion, we saw how the study of tangent lines to functions yields rich information about functions. We now consider the second situation that arises in Calculus, the central problem of finding the area under the curve of a function
Area Under a Curve
First let’s describe what we mean when we refer to the area under a curve. Let’s reconsider our basic quadratic function
We see the crosshatched region that lies between the graph and the
Can you think of any ways that you would be able to approximate the area? (Answer: One ideas is that we could compute the area of the square that has a corner at
We will use a variation of this covering of the region with quadrilaterals to get better approximations. We will do so by dividing the
We now will construct four rectangles that will serve as the basis for our approximation of the area. The subintervals will serve as the width of the rectangles. We will take the length of each rectangle to be the maximum value of the function in the subinterval. Hence we get the following figure:
If we call the rectangles R1–R4, from left to right, then we have the areas
and
Note that this approximation is very close to our initial approximation of
Can you see how we are going to improve our approximation using successive iterations like we did to approximate the slope of the tangent line? (Answer: we will subdivide the interval from
Example 1:
The following table shows the areas of the rectangles and their sum for rectangles having width
Rectangle 
Area of 

















We call this process of finding the area under a curve integration of
Applications of Integral Calculus
We have not yet developed any computational machinery for computing derivatives and integrals so we will just state one popular application of integral calculus that relates the derivative and integrals of a function.
Example 2:
There are quite a few applications of calculus in business. One of these is the cost function
Lesson Summary
 We used linear approximations to study the limit process.
 We computed approximations for the slope of tangent lines to a graph.
 We analyzed applications of differential calculus.
 We analyzed applications of integral calculus.
Review Questions
 For the function
f(x)=x2 approximate the slope of the tangent line to the graph at the point(3,9).  Use the following set of
x− values to generate the sequence of secant line slopes:x=2.9,2.95,2.975,2.995,2.999.  What value does the sequence of slopes approach?
 Use the following set of
 Consider the function
f(x)=x2.  For what values of
x would you expect the slope of the tangent line to be negative?  For what value of
x would you expect the tangent line to have slopem=0 ?  Give an example of a function that has two different horizontal tangent lines?
 For what values of
 Consider the function
p(x)=x3−x. Generate the graph ofp(x) using your calculator. Approximate the slope of the tangent line to the graph at the point
(2,6). Use the following set ofx− values to generate the sequence of secant line slopes.x=2.1,2.05,2.005,2.001,2.0001.  For what values of
x do the tangent lines appear to have slope of0 ? (Hint: Use the calculate function in your calculator to approximate thex− values.)  For what values of
x do the tangent lines appear to have positive slope?  For what values of
x do the tangent lines appear to have negative slope?
 Approximate the slope of the tangent line to the graph at the point
 The cost of producing
x Hi−Fi stereo receivers by Yamaha each week is modeled by the following function:C(x)=850+200x−.3x2.  Generate the graph of
C(x) using your calculator. (Hint: Change your viewing window to reflect the highy values.)  For what number of units will the function be maximized?
 Estimate the slope of the tangent line at
x=200,300,400.  Where is marginal cost positive?
 Generate the graph of
 Find the area under the curve of
f(x)=x2 fromx=1 tox=3. Use a rectangle method that uses the minimum value of the function within subintervals. Produce the approximation for each case of the subinterval cases. four subintervals.
 eight subintervals.
 Repeat part a. using a MidPoint Value of the function within each subinterval.
 Which of the answers in a.  c. provide the best estimate of the actual area?
 Consider the function
p(x)=−x3+4x.  Find the area under the curve from
x=0 tox=1.  Can you find the area under the curve from
x=−1 tox=0. Why or why not? What is problematic for this computation?
 Find the area under the curve from
 Find the area under the curve of
f(x)=x√ fromx=1 tox=4. Use the Max Value rectangle method with six subintervals to compute the area.  The Eiffel Tower is
320meters high. Suppose that you drop a ball off the top of the tower. The distance that it falls is a function of time and is given bys(t)=4.9t2.
Find the velocity of the ball after
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Date Created:
Feb 23, 2012Last Modified:
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