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This module is from Elementary Algebra by Denny Burzynski and Wade Ellis, Jr. Factoring is an essential skill for success in algebra and higher level mathematics courses. Therefore, we have taken great care in developing the student's understanding of the factorization process. The technique is consistently illustrated by displaying an empty set of parentheses and describing the thought process used to discover the terms that are to be placed inside the parentheses.The factoring scheme for special products is presented with both verbal and symbolic descriptions, since not all students can interpret symbolic descriptions alone. Two techniques, the standard "trial and error" method, and the "collect and discard" method (a method similar to the "ac" method), are presented for factoring trinomials with leading coefficients different from 1. Objectives of this module: know how to factor a polynomial using the grouping method and when to try the grouping method.

Overview

  • Using Grouping to Factor a Polynomial
  • Knowing when to Try the Grouping Method

Using grouping to factor a polynomial

Sometimes a polynomial will not have a particular factor common to every term. However, we may still be able to produce a factored form for the polynomial.

The polynomial x 3 3 x 2 6 x 18 has no single factor that is common to every term. However, we notice that if we group together the first two terms and the second two terms, we see that each resulting binomial has a particular factor common to both terms.

The polynomial 'x cubed plus three x squared minus six x minus eighteen'. The first two terms of the polynomial have x square in common, and the last two terms of the polynomial have negative six in common.

Factor x 2 out of the first two terms, and factor 6 out of the second two terms.

x 2 ( x + 3 ) 6 ( x + 3 )

Now look closely at this binomial. Each of the two terms contains the factor ( x + 3 ) .

Factor out ( x + 3 ) .
( x + 3 ) ( x 2 6 ) is the final factorization.

x 3 + 3 x 2 6 x 18 = ( x + 3 ) ( x 2 6 )

Knowing when to try the grouping method

We are alerted to the idea of grouping when the polynomial we are considering has either of these qualities:

  1. no factor common to all terms
  2. an even number of terms

When factoring by grouping, the sign ( + or ) of the factor we are taking out will usually (but not always) be the same as the sign of the first term in that group.

Sample set a

Factor 8 a 2 b 4 4 b 4 + 14 a 2 7 .

  1. We notice there is no factor common to all terms.
  2. We see there are four terms, an even number.
  3. We see that terms 1 and 2 have + 4 b 4 in common (since the 1st term in the group is + 8 a 2 b 4 ) .
  4. We notice that the 3rd and 4th terms have + 7 in common (since the 1st term in the group is + 14 a 2 ).

    The equation eight a squared b to the fourth power minus four b to the fourth power plus fourteen a squared minus seven equals the sum of the product of four b to the fourth power and two a square minus one, and the product of seven and two a square minus 1. The two terms on the right side have two a square minus one in common. 8 a 2 b 4 4 b 4 + 14 a 2 7 = (2a 2 -1)(4b 4 +7)

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Practice set a

Use the grouping method to factor the following polynomials.

a x a y b x b y

( a + b ) ( x + y )

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2 a m + 8 m + 5 a n + 20 n

( 2 m + 5 n ) ( a + 4 )

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a 2 x 3 + 4 a 2 y 3 + 3 b x 3 + 12 b y 3

( a 2 + 3 b ) ( x 3 + 4 y 3 )

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15 m x + 10 n x 6 m y 4 n y

( 5 x 2 y ) ( 3 m + 2 n )

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40 a b x 24 a b x y 35 c 2 x + 21 c 2 x y

x ( 8 a b 7 c 2 ) ( 5 3 y )

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When factoring the polynomial 8 a 2 b 4 4 b 4 14 a 2 7 in Sample Set A, we grouped together terms1 and 2 and 3 and 4. Could we have grouped together terms1 and 3 and 2 and 4? Try this.
8 a 2 b 4 4 b 4 + 14 a 2 7 =

yes

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Do we get the same result? If the results do not look precisely the same, recall the commutative property of multiplication.

Exercises

For the following problems, use the grouping method to factor the polynomials. Some polynomials may not be factorable using the grouping method.

2 a b + 3 a + 18 b + 27

( 2 b + 3 ) ( a + 9 )

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x y 7 x + 4 y 28

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x y + x + 3 y + 3

( y + 1 ) ( x + 3 )

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m p + 3 m q + n p + 3 n q

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a r + 4 a s + 5 b r + 20 b s

( a + 5 b ) ( r + 4 s )

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14 a x 6 b x + 21 a y 9 b y

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12 m x 6 b x + 21 a y 9 b y

3 ( 4 m x 2 b x + 7 a y 3 b y )  Not factorable by grouping

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36 a k 8 a h 27 b k + 6 b h

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a 2 b 2 + 2 a 2 + 3 b 2 + 6

( a 2 + 3 ) ( b 2 + 2 )

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3 n 2 + 6 n + 9 m 3 + 12 m

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8 y 4 5 y 3 + 12 z 2 10 z

Not factorable by grouping

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x 2 3 x + x y 3 y

( x + y ) ( x 3 )

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2 n 2 + 12 n 5 m n 30 m

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4 p q 7 p + 3 q 2 21

Not factorable by grouping

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8 x 2 + 16 x y 5 x 10 y

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12 s 2 27 s 8 s t + 18 t

( 4 s 9 ) ( 3 s 2 t )

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15 x 2 12 x 10 x y + 8 y

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a 4 b 4 + 3 a 5 b 5 + 2 a 2 b 2 + 6 a 3 b 3

a 2 b 2 ( a 2 b 2 + 2 ) ( 1 + 3 a b )

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4 a 3 b c 14 a 2 b c 3 + 10 a b c 2 35 b c 4

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5 x 2 y 3 z + 3 x 3 y w 10 y 3 z 2 6 w x y z

y ( 5 y 2 z + 3 x w ) ( x 2 2 z )

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a 3 b 2 c d + a b c 2 d x a 2 b x y c x 2 y

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5 m 10 n 17 p 3 m 6 n 7 p 4 40 m 4 n 10 q t 2 + 8 p q t 2

( m 6 n 7 p 3 8 q t 2 ) ( 5 m 4 n 10 p )

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Exercises for review

( [link] ) Simplify ( x 5 y 3 ) ( x 2 y ) .

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( [link] ) Use scientific notation to find the product of ( 3 × 10 5 ) ( 2 × 10 2 ) .

6 × 10 3

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( [link] ) Find the domain of the equation y = 6 x + 5 .

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( [link] ) Construct the graph of the inequality y 2 .

A horizontal line with arrows on both ends.

A number line with arrows on each end, labeled from negative three to three in increments of one. There is a closed circle at negative two. A dark arrow is originating from this circle, and heading towrads the right of negative two.

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( [link] ) Factor 8 a 4 b 4 + 12 a 3 b 5 8 a 2 b 3 .

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Questions & Answers

how does the planets on our solar system orbit
cheten Reply
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Issan Reply
Astronomy (from Ancient Greek ἀστρονομία (astronomía) 'science that studies the laws of the stars') is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution.
Rafael
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Elgoog
what is big bang theory?
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No
Richard
the big bang theory is a theory which states that all matter was compressed together in one place the matter got so unstable it exploded releasing All its contents in the form of hydrogen
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I want to be an astronomer. That's my dream
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Who named the the whole galaxy?
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solar Univers
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what are the factors upon which the atmosphere is stratified
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is the big bang the sun
Folakemi Reply
no
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bigbang is the beginning of the universe
Sokak
but thats just a theory
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nothing will happen, don't worry brother.
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what does comet means
GANGAIN Reply
these are Rocky substances between mars and jupiter
GANGAIN
Comets are cosmic snowballs of frozen gases , rock and dust that orbit the sun. They are mostly found between the orbits of Venus and Mercury.
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hey can anyone guide me abt international astronomy olympiad
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how can we learn right and true ?
Govinda Reply
why the moon is always appear in an elliptical shape
Gatjuol Reply
Because when astroid hit the Earth then a piece of elliptical shape of the earth was separated which is now called moon.
Hemen
what's see level?
lidiya Reply
Did you mean eye sight or sea level
Minal
oh sorry it's sea level
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according to the theory of astronomers why the moon is always appear in an elliptical orbit?
Gatjuol
hi !!! I am new in astronomy.... I have so many questions in mind .... all of scientists of the word they just give opinion only. but they never think true or false ... i respect all of them... I believes whole universe depending on true ...থিউরি
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we're all stars and galaxies a part of sun. how can science prove thx with respect old ancient times picture or books..or anything with respect to present time .but we r a part of that universe
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another theory of universe except big ban
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how was universe born
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there many theory to born universe but what is the reality of big bang theory to born universe
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universal
there are many theories regarding this it's on you believe any theory that you think is true ex. eternal inflation theory, oscillation model theory, multiple universe theory the big bang theory etc.
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from where on earth could u observe all the stars during the during the course of an year
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I think it couldn't possible on earth
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in this time i don't Know
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is that so. the question was in the end of this chapter
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in theory, you could see them all from the equator (though over the course of a year, not at pne time). stars are measured in "declination", which is how far N or S of the equator (90* to -90*). Polaris is the North star, and is ALMOST 90* (+89*). So it would just barely creep over the horizon.
Christopher
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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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