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This module is from Elementary Algebra</link>by Denny Burzynski and Wade Ellis, Jr. Methods of solving quadratic equations as well as the logic underlying each method are discussed. Factoring, extraction of roots, completing the square, and the quadratic formula are carefully developed. The zero-factor property of real numbers is reintroduced. The chapter also includes graphs of quadratic equations based on the standard parabola, y = x^2, and applied problems from the areas of manufacturing, population, physics, geometry, mathematics (numbers and volumes), and astronomy, which are solved using the five-step method.Objectives of this module: be able to place a quadratic equation into standard form, be familiar with the zero-factor property of real numbers.

Overview

  • Standard Form of A Quadratic Equation
  • Zero-Factor Property of Real Numbers

Standard form of a quadratic equation

In Chapter ( [link] ) we studied linear equations in one and two variables and methods for solving them. We observed that a linear equation in one variable was any equation that could be written in the form a x + b = 0 , a 0 , and a linear equation in two variables was any equation that could be written in the form a x + b y = c , where a and b are not both 0. We now wish to study quadratic equations in one variable.

Quadratic equation

A quadratic equation is an equation of the form a x 2 + b x + c = 0 , a 0.

The standard form of the quadratic equation is a x 2 + b x + c = 0 , a 0.

For a quadratic equation in standard form a x 2 + b x + c = 0 ,

a is the coefficient of x 2 .
b is the coefficient of x .
c is the constant term.

Sample set a

The following are quadratic equations.

3 x 2 + 2 x 1 = 0. a = 3 , b = 2 , c = 1.

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5 x 2 + 8 x = 0. a = 5 , b = 8 , c = 0.
Notice that this equation could be written 5 x 2 + 8 x + 0 = 0. Now it is clear that c = 0.

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x 2 + 7 = 0. a = 1 , b = 0 , c = 7.
Notice that this equation could be written x 2 + 0 x + 7 = 0. Now it is clear that b = 0.

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The following are not quadratic equations.

3 x + 2 = 0. a = 0. This equation is linear .

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8 x 2 + 3 x 5 = 0.
The expression on the left side of the equal sign has a variable in the denominator and, therefore, is not a quadratic.

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Practice set a

Which of the following equations are quadratic equations? Answer “yes” or “no” to each equation.

6 x 2 4 x + 9 = 0

yes

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4 x 3 5 x 2 + x + 6 = 8

no

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4 x 2 2 x + 4 = 1

yes

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2 x 5 x 2 = 6 x + 4

no

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9 x 2 2 x + 6 = 4 x 2 + 8

yes

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Zero-factor property

Our goal is to solve quadratic equations. The method for solving quadratic equations is based on the zero-factor property of real numbers. We were introduced to the zero-factor property in Section [link] . We state it again.

Zero-factor property

If two numbers a and b are multiplied together and the resulting product is 0, then at least one of the numbers must be 0. Algebraically, if a · b = 0 , then a = 0 or b = 0 , or both a = 0 and b = 0.

Sample set b

Use the zero-factor property to solve each equation.

If 9 x = 0 , then  x  must be  0.

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If 2 x 2 = 0 , then x 2 = 0 , x = 0.

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If 5 ( x 1 ) = 0 , then x 1 must be 0, since 5 is not zero.

x 1 = 0 x = 1

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If x ( x + 6 ) = 0 , then

x = 0 or x + 6 = 0 x = 6 x = 0 , 6.

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If ( x + 2 ) ( x + 3 ) = 0 , then

x + 2 = 0 or x + 3 = 0 x = 2 x = 3 x = 2 , 3.

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If ( x + 10 ) ( 4 x 5 ) = 0 , then

x + 10 = 0 or 4 x 5 = 0 x = 10 4 x = 5 x = 5 4 x = 10 , 5 4 .

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Practice set b

Use the zero-factor property to solve each equation.

( y + 6 ) ( y 7 ) = 0

y = 6 , 7

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( x + 5 ) ( 3 x 4 ) = 0

x = 5 , 4 3

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Exercises

For the following problems, write the values of a , b , and c in quadratic equations.

3 x 2 + 4 x 7 = 0

3 , 4 , 7

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2 y 2 5 y + 5 = 0

2 , 5 , 5

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3 a 2 + 4 a 1 = 0

3 , 4 , 1

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8 a 2 2 a = 0

8 , 2 , 0

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5 x 2 3 x + 9 = 4 x 2

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7 x 2 + 2 x + 1 = 6 x 2 + x 9

1, 1, 10

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3 x 2 + 4 x 1 = 4 x 2 4 x + 12

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5 x 7 = 3 x 2

3 , 5 , 7

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3 x 7 = 2 x 2 + 5 x

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0 = x 2 + 6 x 1

1 , 6 , 1

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For the following problems, use the zero-factor property to solve the equations.

3 ( k + 7 ) = 0

k = 7

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5 ( x + 4 ) = 0

x = 4

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y ( y 1 ) = 0

y = 0 , 1

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n ( n + 4 ) = 0

n = 0 , 4

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x ( x + 7 ) = 0

x = 7 or x = 0

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( y 4 ) ( y 8 ) = 0

y = 4 or y = 8

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( k 1 ) ( k 6 ) = 0

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( x + 5 ) ( x + 4 ) = 0

x = 4 or x = 5

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( y + 6 ) ( 2 y + 1 ) = 0

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( x 3 ) ( 5 x 6 ) = 0

x = 6 5 or x = 3

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( 5 a + 1 ) ( 2 a 3 ) = 0

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( 6 m + 5 ) ( 11 m 6 ) = 0

m = 5 6 or m = 6 11

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( 2 m 1 ) ( 3 m + 8 ) = 0

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( 4 x + 5 ) ( 2 x 7 ) = 0

x = 5 4 , 7 2

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( 3 y + 1 ) ( 2 y + 1 ) = 0

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( 7 a + 6 ) ( 7 a 6 ) = 0

a = 6 7 , 6 7

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( 8 x + 11 ) ( 2 x 7 ) = 0

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( 5 x 14 ) ( 3 x + 10 ) = 0

x = 14 5 , 10 3

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( 3 x 1 ) ( 3 x 1 ) = 0

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( 2 y + 5 ) ( 2 y + 5 ) = 0

y = 5 2

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( 5 m 6 ) 2 = 0

m = 6 5

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Exercises for review

( [link] ) Factor 12 a x 3 x + 8 a 2 by grouping.

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( [link] ) Construct the graph of 6 x + 10 y 60 = 0.
An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

A graph of a line passing through two points coordinates zero, six and five, three.

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( [link] ) Find the difference: 1 x 2 + 2 x + 1 1 x 2 1 .

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( [link] ) Simplify 7 ( 2 + 2 ) .

14 + 2 7

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( [link] ) Solve the radical equation 3 x + 10 = x + 4.

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Questions & Answers

Ayele, K., 2003. Introductory Economics, 3rd ed., Addis Ababa.
Widad Reply
can you send the book attached ?
Ariel
?
Ariel
What is economics
Widad Reply
the study of how humans make choices under conditions of scarcity
AI-Robot
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn Reply
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn
what is ecnomics
Jan Reply
this is the study of how the society manages it's scarce resources
Belonwu
what is macroeconomic
John Reply
macroeconomic is the branch of economics which studies actions, scale, activities and behaviour of the aggregate economy as a whole.
husaini
etc
husaini
difference between firm and industry
husaini Reply
what's the difference between a firm and an industry
Abdul
firm is the unit which transform inputs to output where as industry contain combination of firms with similar production 😅😅
Abdulraufu
Suppose the demand function that a firm faces shifted from Qd  120 3P to Qd  90  3P and the supply function has shifted from QS  20  2P to QS 10  2P . a) Find the effect of this change on price and quantity. b) Which of the changes in demand and supply is higher?
Toofiq Reply
explain standard reason why economic is a science
innocent Reply
factors influencing supply
Petrus Reply
what is economic.
Milan Reply
scares means__________________ends resources. unlimited
Jan
economics is a science that studies human behaviour as a relationship b/w ends and scares means which have alternative uses
Jan
calculate the profit maximizing for demand and supply
Zarshad Reply
Why qualify 28 supplies
Milan
what are explicit costs
Nomsa Reply
out-of-pocket costs for a firm, for example, payments for wages and salaries, rent, or materials
AI-Robot
concepts of supply in microeconomics
David Reply
economic overview notes
Amahle Reply
identify a demand and a supply curve
Salome Reply
i don't know
Parul
there's a difference
Aryan
Demand curve shows that how supply and others conditions affect on demand of a particular thing and what percent demand increase whith increase of supply of goods
Israr
Hi Sir please how do u calculate Cross elastic demand and income elastic demand?
Abari
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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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