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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

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In economics, a perfect market refers to a theoretical construct where all participants have perfect information, goods are homogenous, there are no barriers to entry or exit, and prices are determined solely by supply and demand. It's an idealized model used for analysis,
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When MP₁ becomes negative, TP start to decline. Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 • Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of lab
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Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 • Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of labour (APL) and marginal product of labour (MPL)
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Quantity demanded refers to the specific amount of a good or service that consumers are willing and able to purchase at a give price and within a specific time period. Demand, on the other hand, is a broader concept that encompasses the entire relationship between price and quantity demanded
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Economic growth as an increase in the production and consumption of goods and services within an economy.but Economic development as a broader concept that encompasses not only economic growth but also social & human well being.
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In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities, where neither p
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In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities,
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Suppose a consumer consuming two commodities X and Y has The following utility function u=X0.4 Y0.6. If the price of the X and Y are 2 and 3 respectively and income Constraint is birr 50. A,Calculate quantities of x and y which maximize utility. B,Calculate value of Lagrange multiplier. C,Calculate quantities of X and Y consumed with a given price. D,alculate optimum level of output .
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suppose the production function is given by ( L, K)=L¼K¾.assuming capital is fixed find APL and MPL. consider the following short run production function:Q=6L²-0.4L³ a) find the value of L that maximizes output b)find the value of L that maximizes marginal product
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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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