Intermediate Algebra (11th edition)

64.The surface area of the box with open top shown in the figure is 161. Find the

dimensions of the base. (Hint:The surface area of the box is a function defined by

S 1 x 2 =x^2 + 16 x.)

in.^2

352 CHAPTER 6 Factoring

x

x

44

4 4

65.If an object is projected upward with an initial velocity of 64 ft per sec from a height of

80 ft, then its height in feet tseconds after it is projected is a function defined by

.

How long after it is projected will it hit the ground? (Hint:When it hits the ground, its

height is 0 ft.)

66.Refer to Example 8.After how many seconds will the rocket be

(a)240 ft above the ground?

(b)112 ft above the ground?

67.If a baseball is dropped from a helicopter 625 ft above the ground, then its distance in feet

from the ground tseconds later is a function defined by

.

How long after it is dropped will it hit the ground?

68.If a rock is dropped from a building 576 ft high, then its distance in feet from the ground

tseconds later is a function defined by

.

How long after it is dropped will it hit the ground?

Solve each equation for the specified variable. See Example 9.

69. for r 70. for p


70. for y 72. for t

73.Concept Check Suppose a student solved the formula for L

as follows.

WHAT WENT WRONG?

74.Concept Check Which one of the following is the correct result for solving the following

equation for t?

A. B. C. D.t=

kt-c

2

t=

2 t+c

k

t=

c-kt

• 2

t=

• c
  2 - k

2 t+c=kt

a- 2 LW- 2 HW

2 H

=L

a- 2 LW- 2 HW= 2 LH

a= 2 HW+ 2 LW+ 2 LH

a= 2 HW+ 2 LW+ 2 LH

c=

• 2 t+ 4
  t

w=

3 y-x

y

2 k+ar=r- 3 y 4 s+ 7 p=tp- 7

ƒ 1 t 2 =- 16 t^2 + 576

ƒ 1 t 2 =- 16 t^2 + 625

(^) ƒ 1 t 2 =- 16 t (^2) + 64 t+ 80