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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 construct the graph of a parabola.

Overview

  • Parabolas
  • Constructing Graphs of Parabolas

Parabolas

We will now study the graphs of quadratic equations in two variables with general form y = a x 2 + b x + c , a 0 , a , b , c are real numbers

Parabola

All such graphs have a similar shape. The graph of a quadratic equation of this type Parabola is called a parabola and it will assume one of the following shapes.

Two parabolas, one opening upward and one opening downward. The lowest point of the parabola opening upward and the highest point of the parabola opening downward are each labeled as 'Vertex.'

Vertex

The high point or low point of a parabola is called the vertex of the parabola.

Constructing graphs of parabolas

We will construct the graph of a parabola by choosing several x -values, computing to find the corresponding y -values, plotting these ordered pairs, then drawing a smooth curve through them.

Sample set a

Graph y = x 2 .    Construct a table to exhibit several ordered pairs.

x y = x 2
0 0
1 1
2 4
3 9
1 1
2 4
3 9


A graph of a parabola passing through five points with coordinates negative two, four; negative one, one; zero, zero; one, one; and two, four.

This is the most basic parabola. Although other parabolas may be wider, narrower, moved up or down, moved to the left or right, or inverted, they will all have this same basic shape. We will need to plot as many ordered pairs as necessary to ensure this basic shape.

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Graph y = x 2 2 .     Construct a table of ordered pairs.

x y = x 2 2
0 2
1 1
2 2
3 7
1 1
2 2
3 7


A graph of a parabola passing through five points with coordinates negative two, two; negative one , negative one; zero, negative two, one, negative one; and two, two.

Notice that the graph of y = x 2 2 is precisely the graph of y = x 2 but translated 2 units down. Compare the equations y = x 2 and y = x 2 2 . Do you see what causes the 2 unit downward translation?

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Practice set a

Use the idea suggested in Sample Set A to sketch (quickly and perhaps not perfectly accurately) the graphs of

y = x 2 + 1 and y = x 2 3

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.    An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

A graph of a quadratic equation y equals x square plus one passing through five points with coordinates negative two, five; negative one, two; zero, one; one, two; and two, five.    A graph of a quadratic equation y equals x square minus three passing through five points with coordinates negative two, one; negative one, negative two; zero, negative three; one, negative two; and two, one.

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Sample set b

Graph y = ( x + 2 ) 2 .

Do we expect the graph to be similar to the graph of y = x 2 ? Make a table of ordered pairs.

x y
0 4
1 9
1 1
2 0
3 1
4 4


A graph of a parabola passing through five points with coordinates negative four, four; negative three, one; negative two, zero;negative one, one; and zero, four.

Notice that the graph of y = ( x + 2 ) 2 is precisely the graph of y = x 2 but translated 2 units to the left. The +2 inside the parentheses moves y = x 2 two units to the left. A negative value inside the parentheses makes a move to the right.

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Practice set b

Use the idea suggested in Sample Set B to sketch the graphs of

y = ( x 3 ) 2 and y = ( x + 1 ) 2

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

A graph of a quadratic equation y equals x minus three the whole square passing through five points  with the coordinates one, four; two, one; three, zero; four, one; and five, four.    A graph of a quadratic equation y equals x plus one the whole square passing through five points  with the coordinates negative three, four; negative two, one; negative one, zero; zero, one; and one, four.

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Graph y = ( x 2 ) 2 + 1

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

A graph of a quadratic equation y equals x square minus three passing through five points with the coordinates zero, five; one, two; two, one; three, two; and four, five.

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Exercises

For the following problems, graph the quadratic equations.

y = ( x 1 ) 2

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

y = ( x 1 ) 2

A graph of a parabola passing through five points with coordinates negative one, four; zero, one; one, zero, two, one; and three, four.

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y = ( x + 3 ) 2

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

y = ( x + 3 ) 2

A graph of a parabola passing through five points with coordinates negative five, four; negative four, one; negative three,zero; negative two, one; and negative one, four.

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y = x 2 3

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

y = x 2 3

A graph of a parabola passing through seven points with coordinates negative three, six; negative two, one; negative one, negative two; zero, negative three; one, negative two; two, one; and three, six.

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y = x 2 1 2

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

y = x 2 1 2

A graph of a parabola passing through five points with coordinates negative two, seven over two; negative one, one over two; zero, negative one over two; one, one over two; and two, seven over two.

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y = x 2 + 1 (Compare with problem 2.)

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

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y = x 2 1 (Compare with problem 1.)

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

y = x 2 1

A graph of a parabola passing through five points with coordinates negative two, negative five; negative one, negative two; zero, negative one, one, negative two; and two, negative five.

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y = ( x + 3 ) 2 + 2

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

y = ( x + 3 ) 2 + 2

A graph of a parabola passing through five points with coordinates negative five, six; negative four, three; negative three, two; negative two, three; and negative one, six.

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y = ( x + 3 ) 2

An xy coordinate plane with gridlines, labeled negative five and five with increments of one units on both axes.

y = ( x + 3 ) 2

A graph of a parabola passing through five points with coordinates negative five, negative four; negative four, negative one; negative three, zero; negative two, negative one; and negative one, negative four.

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For the following problems, try to guess the quadratic equation that corresponds to the given graph.

Exercises for review

( [link] ) Simplify and write ( x 4 y 5 ) 3 ( x 6 y 4 ) 2 so that only positive exponents appear.

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( [link] ) Factor y 2 y 42.

( y + 6 ) ( y 7 )

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( [link] ) Find the sum: 2 a 3 + 3 a + 3 + 18 a 2 9 .

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( [link] ) Simplify 2 4 + 5 .

8 2 5 11

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( [link] ) Four is added to an integer and that sum is doubled. When this result is multiplied by the original integer, the product is 6. Find the integer.

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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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