Beginning Algebra, 11th Edition

36.If an object is projected upward from ground level with
an initial velocity of 64 ft per sec, its height hin feet
tseconds later is
.
(a)After how many seconds is the height 48 ft?
(b)The object reaches its maximum height 2 sec after
it is projected. What is this maximum height?
(c) After how many seconds does the object hit the ground?
(d)Find the number of seconds after which the height is 60 ft.
(e) What is the physical interpretation of why part (d) has two answers?
(f ) The quadratic equation from part (c) has two solutions, yet only one of them is
appropriate for answering the question. Why is this so?

37.The table shows the number of cellular phone subscribers (in millions) in the United States.

h=- 16 t^2 + 64 t

SECTION 6.6 Applications of Quadratic Equations 409

Year Subscribers (in millions)

1990 5

1992 11

1994 24

1996 44

1998 69

2000 109

2002 141

2004 182

2006 233

2008 263

We used the preceding data to develop the quadratic equation

which models the number yof cellular phone subscribers (in millions) in the year x, where

represents 1990, represents 1992, and so on.

(a)Use the model to find the number of subscribers in 2000, to the nearest tenth. How

does the result compare with the actual data in the table?

(b)What value of xcorresponds to 2008?

(c) Use the model to find the number of cellular phone subscribers in 2008, to the nearest

tenth. How does the result compare with the actual data in the table?

(d)Assuming that the trend in the data continues, use the quadratic equation to estimate

the number of cellular phone subscribers in 2010, to the nearest tenth.

38.Annual revenue in billions of dollars for eBay is shown in the table.

x= 0 x= 2

y=0.590x^2 +4.523x+0.136,

Source:CTIA—The Wireless

Association.

Source: eBay.

Annual Revenue

Year (in billions of dollars)

2002 1.21

2003 2.17

2004 3.27

2005 4.55

2006 5.97

2007 7.67