Beginning Algebra, 11th Edition

63.The area of a circle with radius ris
given by the formula

If a circle has area 81 , what is its

radius?

64.The surface area Sof a sphere with ra-

dius ris given by the formula

If a sphere has surface area 36 ,

what is its radius?

p ft^2

S= 4 pr^2.

p in.^2

a=pr^2.

a

SECTION 9.1 Solving Quadratic Equations by the Square Root Property 559

r

a = r^2

r

S = 4r^2

The amount A that P dollars invested at an annual rate of interest r will grow to in 2 yr is

65.At what interest rate will $100 grow to $104.04 in 2 yr?

66.At what interest rate will $500 grow to $530.45 in 2 yr?

A=P 11 +r 22.

Simplify all radicals, and combine like terms. Express fractions in lowest terms. See
Sections 8.3 and 8.4.

Factor each perfect square trinomial. See Section 6.4.

70. 
    
    
    
    71. 72.z^2 +z+
    
    
    
    

1

4

z^2 + 4 z+ 4 x^2 - 10 x+ 25

6 + 224

8

12 - 227

9

4

5

+

B

48

25

PREVIEW EXERCISES

62.The illumination produced by a light source
depends on the distance from the source.
For a particular light source, this relation-
ship can be expressed as

where Iis the amount of illumination in foot-

candles and dis the distance from the light

source (in feet). How far from the source is

the illumination equal to 50 footcandles?

I=

4050

d^2

,

d