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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 recognize square root equations and extraneous solutions, be able to sove square root equations.

Overview

  • Square Root Equations And Extraneous Solutions
  • Method For Solving Square Root Equations

Square root equations and extraneous solutions

Square root equation

A square root equation is an equation that contains a variable under a square root sign. The fact that x · x = ( x ) 2 = x suggests that we can solve a square root equation by squaring both sides of the equation.

Extraneous solutions

Squaring both sides of an equation can, however, introduce extraneous solutions. Consider the equation

x = 6

The solution is 6. Square both sides.

x 2 = ( 6 ) 2
x 2 = 36

This equation has two solutions, 6 and + 6. The + 6 is an extraneous solution since it does not check in the original equation: + 6 6.

Method for solving square root equations

Solving square root equations

  1. Isolate a radical. This means get a square root expression by itself on one side of the equal sign.
  2. Square both sides of the equation.
  3. Simplify the equation by combining like terms.
  4. Repeat step 1 if radicals are still present.
  5. Obtain potential solutions by solving the resulting non-square root equation.
  6. Check each potential solution by substitution into the original equation.

Sample set a

Solve each square root equation.

x = 8. The radical is isolated Square both sides . ( x ) 2 = 8 2 x = 64 Check this potential solution . C h e c k : 64 = 8 Is this correct? 8 = 8 Yes, this is correct. 64 is the solution .

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y - 3 = 4. The radical is isolated. Square both sides . y - 3 = 16 Solve this nonradical equation . y = 19 Check this potential solution . C h e c k : 19 - 3 = 16 Is this correct? 16 = 4 Is this correct? 4 = 4 Yes, this is correct. 19 is the solution .

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2 m + 3 - m - 8 = 0. Isolate either radical . 2 m + 3 = m - 8 Square both sides . 2 m + 3 = m - 8 Solve this nonradical equation . m = - 11 Check this potential solution . C h e c k : 2 ( - 11 ) + 3 - ( - 11 ) - 8 = 0 Is this correct? - 22 + 3 - - 19 = 0 Is this correct?
Since  - 19  is not a real number, the potential solution of  m = - 11  does not check . This equation has no real solution .

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4 x 5 = 6. By inspection, this equation has no real solution .
The symbol, , signifies the positive square root and not the negative square root.

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Practice set a

Solve each square root equation.

3 a + 8 2 a + 5 = 0

a = 3 is extraneous, no real solution

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m 4 = 11

no real solution

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Exercises

For the following problems, solve the square root equations.

y 4 4 = 0

y = 20

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6 m 4 = 5 m 1

m = 3

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7 a + 6 = 3 a 18

no solution

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10 a 7 2 a + 9 = 0

a = 2

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12 k 5 9 k + 10 = 0

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x 6 3 x 8 = 0

no solution

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4 a 5 7 a 20 = 0

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2 m 6 = m 2

m = 4

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3 x + 1 = 2 x 6

no solution

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2 a + 9 a 4 = 0

no solution

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At a certain electronics company, the daily output Q is related to the number of people A on the assembly line by Q = 400 + 10 A + 125 .
(a) Determine the daily output if there are 44 people on the assembly line.

(b) Determine how many people are needed on the assembly line if the daily output is to be 520.

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At a store, the daily number of sales S is approximately related to the number of employees E by S = 100 + 15 E + 6
(a) Determine the approximate number of sales if there are 19 employees.

(b) Determine the number of employees the store would need to produce 310 sales.

( a ) S = 175 ; ( b ) E = 190

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Use a calculator. The resonance frequency f in an electronic circuit containing inductance L and capacitance C in series is given by

f = 1 2 π L C

(a) Determine the resonance frequency in an electronic circuit if the inductance is 4 and the capacitance is 0.0001 . Use π = 3.14.

(b) Determine the inductance in an electric circuit if the resonance frequency is 7.12 and the capacitance is 0.0001 . Use π = 3.14.

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If two magnetic poles of strength m and m ' units are at a distance r centimeters (cm) apart, the force F of repulsion in air between them is given by

F = m m ' r 2

(a) Determine the force of repulsion if two magnetic poles of strengths 20 and 40 units are 5 cm apart in air.

(b) Determine how far apart are two magnetic poles of strengths 30 and 40 units if the force of repulsion in air between them is 0.0001 .

( a ) F = 32 ( b ) r = 8 cm

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The velocity V in feet per second of outflow of a liquid from an orifice is given by V = 8 h , where h is the height in feet of the liquid above the opening.
(a) Determine the velocity of outflow of a liquid from an orifice that is 9 feet below the top surface of a liquid ( V is in feet/sec).

(b) Determine how high a liquid is above an orifice if the velocity of outflow is 81 feet/second.

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Use a calculator. The period T in seconds of a simple pendulum of length L in feet is given by T = 2 π L 32 .

(a) Determine the period of a simple pendulum that is 2 feet long. Use π = 3.14.

(b) Determine the length in feet of a simple pendulum whose period is 10.8772 seconds. Use π = 3.14.

( a ) T = 1.57  sec  ( b ) L = 95.99  cm

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The kinetic energy K E in foot pounds of a body of mass m in slugs moving with a velocity v in feet/sec is given by

K E = 1 2 m v 2

(a) Determine the kinetic energy of a 2-slug body moving with a velocity of 4 ft/sec.

(b) Determine the velocity in feet/sec of a 4-slug body if its kinetic energy is 50 foot pounds.

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Exercises for review

( [link] ) Write x 10 y 3 ( x + 7 ) 4 x 2 y 3 ( x + 7 ) 1 so that only positive exponents appear.

x 12 ( x + 7 ) 5

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( [link] ) Classify x + 4 = x + 7 as an identity, a contradiction, or a conditional equation.

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( [link] ) Supply the missing words. In the coordinate plane, lines with slope rise and lines with slope fall.

positive; negative

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( [link] ) Simplify ( x + 3 ) 4 ( x 2 ) 6 .

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( [link] ) Simplify ( 3 + 5 ) ( 4 5 ) .

7 + 5

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Questions & Answers

how did you get 1640
Noor Reply
If auger is pair are the roots of equation x2+5x-3=0
Peter Reply
Wayne and Dennis like to ride the bike path from Riverside Park to the beach. Dennis’s speed is seven miles per hour faster than Wayne’s speed, so it takes Wayne 2 hours to ride to the beach while it takes Dennis 1.5 hours for the ride. Find the speed of both bikers.
MATTHEW Reply
420
Sharon
from theory: distance [miles] = speed [mph] × time [hours] info #1 speed_Dennis × 1.5 = speed_Wayne × 2 => speed_Wayne = 0.75 × speed_Dennis (i) info #2 speed_Dennis = speed_Wayne + 7 [mph] (ii) use (i) in (ii) => [...] speed_Dennis = 28 mph speed_Wayne = 21 mph
George
Let W be Wayne's speed in miles per hour and D be Dennis's speed in miles per hour. We know that W + 7 = D and W * 2 = D * 1.5. Substituting the first equation into the second: W * 2 = (W + 7) * 1.5 W * 2 = W * 1.5 + 7 * 1.5 0.5 * W = 7 * 1.5 W = 7 * 3 or 21 W is 21 D = W + 7 D = 21 + 7 D = 28
Salma
Devon is 32 32​​ years older than his son, Milan. The sum of both their ages is 54 54​. Using the variables d d​ and m m​ to represent the ages of Devon and Milan, respectively, write a system of equations to describe this situation. Enter the equations below, separated by a comma.
Aaron Reply
find product (-6m+6) ( 3m²+4m-3)
SIMRAN Reply
-42m²+60m-18
Salma
what is the solution
bill
how did you arrive at this answer?
bill
-24m+3+3mÁ^2
Susan
i really want to learn
Amira
I only got 42 the rest i don't know how to solve it. Please i need help from anyone to help me improve my solving mathematics please
Amira
Hw did u arrive to this answer.
Aphelele
hi
Bajemah
-6m(3mA²+4m-3)+6(3mA²+4m-3) =-18m²A²-24m²+18m+18mA²+24m-18 Rearrange like items -18m²A²-24m²+42m+18A²-18
Salma
complete the table of valuesfor each given equatio then graph. 1.x+2y=3
Jovelyn Reply
x=3-2y
Salma
y=x+3/2
Salma
Hi
Enock
given that (7x-5):(2+4x)=8:7find the value of x
Nandala
3x-12y=18
Kelvin
please why isn't that the 0is in ten thousand place
Grace Reply
please why is it that the 0is in the place of ten thousand
Grace
Send the example to me here and let me see
Stephen
A meditation garden is in the shape of a right triangle, with one leg 7 feet. The length of the hypotenuse is one more than the length of one of the other legs. Find the lengths of the hypotenuse and the other leg
Marry Reply
how far
Abubakar
cool u
Enock
state in which quadrant or on which axis each of the following angles given measure. in standard position would lie 89°
Abegail Reply
hello
BenJay
hi
Method
I am eliacin, I need your help in maths
Rood
how can I help
Sir
hmm can we speak here?
Amoon
however, may I ask you some questions about Algarba?
Amoon
hi
Enock
what the last part of the problem mean?
Roger
The Jones family took a 15 mile canoe ride down the Indian River in three hours. After lunch, the return trip back up the river took five hours. Find the rate, in mph, of the canoe in still water and the rate of the current.
cameron Reply
Shakir works at a computer store. His weekly pay will be either a fixed amount, $925, or $500 plus 12% of his total sales. How much should his total sales be for his variable pay option to exceed the fixed amount of $925.
mahnoor Reply
I'm guessing, but it's somewhere around $4335.00 I think
Lewis
12% of sales will need to exceed 925 - 500, or 425 to exceed fixed amount option. What amount of sales does that equal? 425 ÷ (12÷100) = 3541.67. So the answer is sales greater than 3541.67. Check: Sales = 3542 Commission 12%=425.04 Pay = 500 + 425.04 = 925.04. 925.04 > 925.00
Munster
difference between rational and irrational numbers
Arundhati Reply
When traveling to Great Britain, Bethany exchanged $602 US dollars into £515 British pounds. How many pounds did she receive for each US dollar?
Jakoiya Reply
how to reduced echelon form
Solomon Reply
Jazmine trained for 3 hours on Saturday. She ran 8 miles and then biked 24 miles. Her biking speed is 4 mph faster than her running speed. What is her running speed?
Zack Reply
d=r×t the equation would be 8/r+24/r+4=3 worked out
Sheirtina
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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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