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This module is from Elementary Algebra by Denny Burzynski and Wade Ellis, Jr. The distinction between the principal square root of the number x and the secondary square root of the number x is made by explanation and by example. The simplification of the radical expressions that both involve and do not involve fractions is shown in many detailed examples; this is followed by an explanation of how and why radicals are eliminated from the denominator of a radical expression. Real-life applications of radical equations have been included, such as problems involving daily output, daily sales, electronic resonance frequency, and kinetic energy.Objectives of this module: be able to use the product property of square roots to multiply square roots.

Overview

  • The Product Property of Square Roots
  • Multiplication Rule for Square Root Expressions

The product property of square roots

In our work with simplifying square root expressions, we noted that

x y = x y

Since this is an equation, we may write it as

x y = x y

To multiply two square root expressions, we use the product property of square roots.

The product property x y = x y

x y = x y

The product of the square roots is the square root of the product.

In practice, it is usually easier to simplify the square root expressions before actually performing the multiplication. To see this, consider the following product:

8 48
We can multiply these square roots in either of two ways:

Simplify then multiply.

4 · 2 16 · 3 = ( 2 2 ) ( 4 3 ) = 2 · 4 2 · 3 = 8 6

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Multiply then simplify.

8 48 = 8 · 48 = 384 = 64 · 6 = 8 6

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Notice that in the second method, the expanded term (the third expression, 384 ) may be difficult to factor into a perfect square and some other number.

Multiplication rule for square root expressions

The preceding example suggests that the following rule for multiplying two square root expressions.

Rule for multiplying square root expressions

  1. Simplify each square root expression, if necessary.
  2. Perform the multiplecation.
  3. Simplify, if necessary.

Sample set a

Find each of the following products.

3 6 = 3 · 6 = 18 = 9 · 2 = 3 2

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8 2 = 2 2 2 = 2 2 · 2 = 2 4 = 2 · 2 = 4

This product might be easier if we were to multiply first and then simplify.

8 2 = 8 · 2 = 16 = 4

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20 7 = 4 5 7 = 2 5 · 7 = 2 35

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5 a 3 27 a 5 = ( a 5 a ) ( 3 a 2 3 a ) = 3 a 3 15 a 2 = 3 a 3 · a 15 = 3 a 4 15

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( x + 2 ) 7 x 1 = ( x + 2 ) 6 ( x + 2 ) x 1 = ( x + 2 ) 3 ( x + 2 ) x 1 = ( x + 2 ) 3 ( x + 2 ) ( x 1 ) or = ( x + 2 ) 3 x 2 + x 2

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Practice set a

Find each of the following products.

x + 4 x + 3

( x + 4 ) ( x + 3 )

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8 m 5 n 20 m 2 n

4 m 3 n 10 m

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9 ( k 6 ) 3 k 2 12 k + 36

3 ( k 6 ) 2 k 6

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2 a ( 5 a 8 a 3 )

a 10 4 a 2

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32 m 5 n 8 ( 2 m n 2 10 n 7 )

8 m 3 n 2 n 8 m 2 n 5 5 m

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Exercises

x + 2 x 3

( x + 2 ) ( x 3 )

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y + 3 y 2

( y + 3 ) ( y 2 )

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x + 9 ( x + 9 ) 2

( x + 9 ) x + 9

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3 a 2 15 a 3

3 a 2 5 a

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12 ( p q ) 3 3 ( p q ) 5

6 ( p q ) 4

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15 a 2 ( b + 4 ) 4 21 a 3 ( b + 4 ) 5

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125 m 5 n 4 r 8 8 m 6 r

10 m 5 n 2 r 4 10 m r

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7 ( 2 k 1 ) 11 ( k + 1 ) 3 14 ( 2 k 1 ) 10

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2 a 4 5 a 3 2 a 7

2 a 7 5

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2 m 3 n + 1 10 m n + 3

2 m 2 n + 2 5

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75 ( a 2 ) 7 48 a 96

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8 ( a 3 a )

2 2 a 2 6 a

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y ( y 5 + 3 y 3 )

y 2 ( y + 3 )

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8 a 5 ( 2 a 6 a 11 )

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12 m 3 ( 6 m 7 3 m )

6 m 2 ( m 3 2 1 )

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5 x 4 y 3 ( 8 x y 5 7 x )

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Exercises for review

( [link] ) Factor a 4 y 4 25 w 2 .

( a 2 y 2 + 5 w ) ( a 2 y 2 5 w )

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( [link] ) Find the slope of the line that passes through the points ( 5 , 4 ) and ( 3 , 4 ) .

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( [link] ) Perform the indicated operations:

15 x 2 20 x 6 x 2 + x 12 · 8 x + 12 x 2 2 x 15 ÷ 5 x 2 + 15 x x 2 25

4 ( x + 5 ) ( x + 3 ) 2

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( [link] ) Simplify x 4 y 2 z 6 by removing the radical sign.

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( [link] ) Simplify 12 x 3 y 5 z 8 .

2 x y 2 z 4 3 x y

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Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
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2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
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Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
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Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
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A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
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Source:  OpenStax, Elementary algebra. OpenStax CNX. May 08, 2009 Download for free at http://cnx.org/content/col10614/1.3
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