Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 7 - Section 7.1 - Systems of Linear Equations in Two Variables - Exercise Set - Page 821: 80


a. $(2004, 180)$. $2004$, $180$ million b. year $2004$. $180$ million c. very well.

Work Step by Step

a. Based on the given graph, the intersection point can be found to be around $(2004, 180)$. This means that in 2004, the number of cellphone and land-line customers are the same, with about 180 millions of customers for each. b. Based on the first models, we have $ y = 198-4.3x $ for the number of land-line customers, and for the second model $y = 19.8x + 98$. Let $198-4.3x = 19.8x + 98$ we have $24.1x=100$ which gives $x=4.15\approx4$ or year $2004$. At $x=4.15$, we have $y=198-4.3(4.15)\approx180$ million for each model. c. We can see that the model results from part-(b) fit the data from part-(a) very well.
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