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Graph This!

Activity Description Activity GuideProblem


Part 1: Piecewise Graphing

Consider the following dilemma:

In Charlottesville VA there are 2 internet service providers. C-ville OnLine's monthly plan costs $6 for the first 20 hours on line per month, and $1 per each additional hour, with a monthly maximum of $66 per month. The other company, MS Albemarle, charges a monthly connection fee of $2, plus 50 cents for each hour on line with no maximum. Determine the conditions under which each plan is preferable.

(a) Resolve this dilemma algebraically.

(b) Resolve this dilemma graphically.

(c) Comment on the differences between approaches.

Note: Use this task to emphasize the advantages of graphical approaches to solving applied problems, and to introduce piecewise graphing on the graphing calculator.

Part 2: Solving Equations Graphically I

(a) Hypothesize how many solutions there are to the equation X8 = 2X, and algebraically try to find them.

(b) Find all solutions to the equation graphically, and play with the window to explore the graphs.

(c) Comment on the differences between approaches.

(d) Use the equation solver of your graphing calculator to try to find other solutions.

(e) What conclusion can you draw from this exercise?

Note: There are three solutions to this equation. This task shows that students cannot solely rely on the graphs to find all solutions. Also, this task can be used to illustrate exponential growth - the exponential eventually "catches up" and passes the power function.

Part 3: Solving Equations Graphically II

(a) Algebraically, find all solutions to the equation: (X2 -5X +5)^ (X2-9X+20) = 1.

(b) Solve for X graphically - Find a window to display all solutions.

(c) Analyze and discuss the graph obtained in (b)

Note: There are 5 solutions to this equation. This task can be used to discuss issues related to roots, exponents, domain and range, complex numbers, etc.

Part 4: Analyzing Terms Graphically

Consider the following functions: F(X) = 2X2, G(X)=6X, and H(X)=3.

(a) Predict the shapes of the graphs of:

2X2
2X2+ 3
2X2+ 6X +3

(b) Graph each of the three functions specified in task (a) and compare these graphs with your predictions.

(c) Create a table of values of these functions and for F, G, and H for a range of values of X, and relate these values to your graphs and observations.

(d) Comment on your observations.

(e) Vary the coefficient of the linear term in 2X2+6X+3, and predict and explain the resulting graphs.

Part 5: Analyze Factors Graphically

(a) Consider the following equation: (X-1)(X+2)(X-3) = X3-2X2-5X+6 (a) Discuss the relationship between the zeroes of each factor and the zeroes of the product.

(b) Graph each factor function. Analyze the roots and regions where each is positive and negative and predict the graph of the product function.

(c) Graph the product function, together with the graphs of the factor functions.

(d) Discuss your observations.

Part 6: Taylor's Theorem

(a) Determine the first 6 terms of a Taylor series approximation of F(X)=sin(X) around X=0.

(b) Show graphically several Taylor approximations to F(X)=sin(X) around X=0. (e.g., one utilizing only the first term, another utilizing the first 3 terms, another utilizing the first 6 terms).

(c) Create a table containing sin(X) and several Taylor approximations to sin(X) around X=0.

(d) Comment on your observations of the graphs and table of values.

Note: Recall that Sin(X) = X-X3/3!+X5/5!-X7/7!…..

Part 7: Evaluate Expressions Graphically

(a) Algebraically, evaluate the expression: X5+1/X5, when X2+1/X2 = 7.

(b) Evaluate the same expression graphically.

Hint: Draw graphs of both functions and the graph of Y=7, and use the intersection finder and/or trace features of your calculator to go from the intersection of 7 with lower power function to the higher power function.

(c) Comment on the different approaches to evaluating this expression.

Part 8: Finding Limits Graphically

(a) Algebraically, find the limit of A(X) = (X-2)/(X-2) as X approaches to 2. Explore this limit graphically on your calculator. Discuss connections between the graphical and algebraic representations.

(b) Do the same for B(X) = (X2-X-2)/(X-2) as X approaches 2.

(c) Do the same for C(X) = 1/(X-1) as X approaches 1.

(d) Do the same for E(X) = (1+1/X)X as X increases without bound.

(e) Do the same for F(X) = sin(1/X) as X approaches 0.

Part 9: Using Graphs to Solve Max/Min Problems I

Consider the following problem (from Frank Pullano, Winthrop University):

The Mama Mia Sauce Company wants to package their famous sauce in 980 cc cans. They would like to minimize the amount of material used to make the cans. Your job as production manager for Mama Mia is to determine what can dimensions, radius and height, will produce a can which will hold the desired amount of sauce yet use the least amount of material.

(a) Solve this problem using algebraic methods.

(b) Solve this problem by generating a graph of the relationship between the surface area of the can and the radius of the can.

(c) Compare both methods.

Note 1: It is often instructive to have students predict the shape of the graph before graphing it

Note 2: An appropriate graph window is very important here. Students should use a reasonable estimate of the dimensions of a sauce can to help determine a window.

 

Part 10: Using Graphs to Solve Max/Min Problems II

Consider the following situation (from Frank Pullano, Winthrop University):

The marketing director at Mama Mia has recently been given research that leads her to believe that at a price of $2.75 per can of sauce, sales will be 3200 cans per week. The research also indicates that for every $.15 increase in price, sales will drop by 100 cans per week.

(a) Derive a function relating revenue (price per can times the number of cans sold) to the number of 15-cent increments, predict the shape of the graph of this function, and then graph the function.

(b) Use this function to determine: (i) the maximum revenue Mama Mia can expect, (ii) the price per can that yields maximum revenue, and (iii) the number of cans of sauce Mama Mia should expect to sell at this price to achieve maximum revenue.

(c) Discuss the graph, make connections to the algebraic representation, and interpret various regions and points of interest.

Hint:  The general function for revenue can be written as R=(P)(U) where R is revenue, P is price per unit and U is number of units sold. Expressions for price (P) and units sold (U) can be written as P= $2.75 + $.15X and U= 3200 - 100X, where X is the number of 15 cent increments. This leads to a revenue function of R=(2.75 + .15X)(3200 - 100X).

Part 11: Using Graphs to Solve Max/Min Problems II

Consider the following situation (from Frank Pullano, Winthrop University):

Assume that Mama Mia produces only what it can sell and that the cost of production (C) to Mama Mia is $1.35 per can of sauce, regardless of how many cans are produced.

(a) Use the sales forecast in the problem above to derive and graph a function relating total costs to the number of cans of sauce sold in terms of the number of 15-cent increments. Using your functions for revenue and total cost, write a function for profit. How many jars of sauce must Mama Mia sell, and at what price, to maximize profits? What do you notice about the price per jar at maximum revenue compared to the price per jar at maximum profit?

(b) Discuss the graph, make connections to the algebraic representation, and interpret various regions and points of interest.

Hint:  Since profit equals revenue minus cost, one expression for profit is: 
(2.75 + .15X)(3200 - 100X) - 1.35(3200 -100X).

Part 12: Solving a Numberical Comparison Problem Graphically

(a) Algebraically, without calculating these values, determine which is greater eπ or πe.

(b) Solve this problem graphically.

(c) Compare the two approaches.

Hint:  Graph the function ln(X)/ X and analyze the graph.

Part 13: Simulating Exponential Growth

Perform the following demonstration:

Take a sheet on paper, rip it in half, and then pile one half on top of the other. We will now have a pile with height equal to the thickness of two sheets of paper. Take that pile, rip it in half, and pile one half on top of the other. The resulting pile would have height equal to 4 sheets of paper. Continue this process three more times, and show the resulting pile to the class.

(a) Without performing any calculations, estimate the answer the following question: What would be the height of the pile if I continued this process for a total of 50 rips?

(b) Calculate the height of this resulting pile.

Note:  Use .004 inches as the thickness of a piece of paper and use miles as the unit for distance.

(c) Simulate the growth of this pile on your graphing calculator and trace values.

Hint:  Use parametric graphing, with X(t)=1 and Y(t)=(.004/(12*5280))*2t, with t ranging from 1 to 50. For emphasis, display the word SUN on your screen at a distance of approximately 93,000,000 miles.

(d) Comment on the differences between the numerical and graphical solutions.

(e) Comment on your intuition about exponential growth.

Part 15: Graphically Analyzing the World Series

Consider the following problem (from Larry Cavanaugh, Louisa High School, VA):

The World Series is a best-of seven competition. That is, two teams play each other until one of them has won a total of 4 games. Hence, a World Series can be won in as little as four games and in as many as seven games. Suppose that two teams are playing in a World Series and that the probability of Team A beating Team B in any game is p.

(a) Calculate the probability that Team A wins the World Series in 4 games.

(b) Predict the shape of the graph of the relationship between the probability of Team A winning the Series in 4 games and the probability of Team A winning any single game.

(c) Graph this relationship, and analyze the graph.

(d) Discuss your observations.

(e) Suppose that the teams are evenly matched; that is, the probability of each team winning a single game is 50-50. Calculate the probability of that Team A will win in 4 games.

(f) Repeat tasks (a)-(e) for 5 games, 6 games, and 7 games.

(g) Use the results of (e) to show that the overall probability of either winning the Series is also 50-50.

(h) For the above situation, discuss the relationship between the probability of evenly matched teams winning in 6 games or 7 games. 

(i) Overall, regardless of the probability of any team winning a game, what is the expected number of games that need to be played to determine the winner?

Note: When analyzing the graphs generated in Task C, be sure to note what happens when one team has a probability of 0 or a probability of 1 of winning a game.

Hint:  To win in 5 games, a team must win the last game, and 3 of the previous 4 games.




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Last modified on August 15, 2001.