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Given a sum of cubes or difference of cubes, factor it.

  1. Confirm that the first and last term are cubes, a 3 + b 3 or a 3 b 3 .
  2. For a sum of cubes, write the factored form as ( a + b ) ( a 2 a b + b 2 ) . For a difference of cubes, write the factored form as ( a b ) ( a 2 + a b + b 2 ) .

Factoring a sum of cubes

Factor x 3 + 512.

Notice that x 3 and 512 are cubes because 8 3 = 512. Rewrite the sum of cubes as ( x + 8 ) ( x 2 8 x + 64 ) .

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Factor the sum of cubes: 216 a 3 + b 3 .

( 6 a + b ) ( 36 a 2 −6 a b + b 2 )

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Factoring a difference of cubes

Factor 8 x 3 125.

Notice that 8 x 3 and 125 are cubes because 8 x 3 = ( 2 x ) 3 and 125 = 5 3 . Write the difference of cubes as ( 2 x 5 ) ( 4 x 2 + 10 x + 25 ) .

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Factor the difference of cubes: 1,000 x 3 1.

( 10 x 1 ) ( 100 x 2 + 10 x + 1 )

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Factoring expressions with fractional or negative exponents

Expressions with fractional or negative exponents can be factored by pulling out a GCF. Look for the variable or exponent that is common to each term of the expression and pull out that variable or exponent raised to the lowest power. These expressions follow the same factoring rules as those with integer exponents. For instance, 2 x 1 4 + 5 x 3 4 can be factored by pulling out x 1 4 and being rewritten as x 1 4 ( 2 + 5 x 1 2 ) .

Factoring an expression with fractional or negative exponents

Factor 3 x ( x + 2 ) −1 3 + 4 ( x + 2 ) 2 3 .

Factor out the term with the lowest value of the exponent. In this case, that would be ( x + 2 ) 1 3 .

( x + 2 ) 1 3 ( 3 x + 4 ( x + 2 ) ) Factor out the GCF . ( x + 2 ) 1 3 ( 3 x + 4 x + 8 ) Simplify . ( x + 2 ) 1 3 ( 7 x + 8 )
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Factor 2 ( 5 a 1 ) 3 4 + 7 a ( 5 a 1 ) 1 4 .

( 5 a −1 ) 1 4 ( 17 a −2 )

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Access these online resources for additional instruction and practice with factoring polynomials.

Key equations

difference of squares a 2 b 2 = ( a + b ) ( a b )
perfect square trinomial a 2 + 2 a b + b 2 = ( a + b ) 2
sum of cubes a 3 + b 3 = ( a + b ) ( a 2 a b + b 2 )
difference of cubes a 3 b 3 = ( a b ) ( a 2 + a b + b 2 )
  • The greatest common factor, or GCF, can be factored out of a polynomial. Checking for a GCF should be the first step in any factoring problem. See [link] .
  • Trinomials with leading coefficient 1 can be factored by finding numbers that have a product of the third term and a sum of the second term. See [link] .
  • Trinomials can be factored using a process called factoring by grouping. See [link] .
  • Perfect square trinomials and the difference of squares are special products and can be factored using equations. See [link] and [link] .
  • The sum of cubes and the difference of cubes can be factored using equations. See [link] and [link] .
  • Polynomials containing fractional and negative exponents can be factored by pulling out a GCF. See [link] .

Verbal

If the terms of a polynomial do not have a GCF, does that mean it is not factorable? Explain.

The terms of a polynomial do not have to have a common factor for the entire polynomial to be factorable. For example, 4 x 2 and −9 y 2 don’t have a common factor, but the whole polynomial is still factorable: 4 x 2 −9 y 2 = ( 2 x + 3 y ) ( 2 x −3 y ) .

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A polynomial is factorable, but it is not a perfect square trinomial or a difference of two squares. Can you factor the polynomial without finding the GCF?

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How do you factor by grouping?

Divide the x term into the sum of two terms, factor each portion of the expression separately, and then factor out the GCF of the entire expression.

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Algebraic

For the following exercises, find the greatest common factor.

14 x + 4 x y 18 x y 2

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49 m b 2 35 m 2 b a + 77 m a 2

7 m

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30 x 3 y 45 x 2 y 2 + 135 x y 3

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200 p 3 m 3 30 p 2 m 3 + 40 m 3

10 m 3

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36 j 4 k 2 18 j 3 k 3 + 54 j 2 k 4

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6 y 4 2 y 3 + 3 y 2 y

y

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For the following exercises, factor by grouping.

2 a 2 + 9 a 18

( 2 a −3 ) ( a + 6 )

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6 n 2 19 n 11

( 3 n −11 ) ( 2 n + 1 )

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2 p 2 5 p 7

( p + 1 ) ( 2 p −7 )

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For the following exercises, factor the polynomial.

10 h 2 9 h 9

( 5 h + 3 ) ( 2 h −3 )

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9 d 2 −73 d + 8

( 9 d −1 ) ( d −8 )

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12 t 2 + t 13

( 12 t + 13 ) ( t −1 )

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16 x 2 100

( 4 x + 10 ) ( 4 x 10 )

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121 p 2 169

( 11 p + 13 ) ( 11 p 13 )

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361 d 2 81

( 19 d + 9 ) ( 19 d 9 )

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144 b 2 25 c 2

( 12 b + 5 c ) ( 12 b 5 c )

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49 n 2 + 168 n + 144

( 7 n + 12 ) 2

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225 y 2 + 120 y + 16

( 15 y + 4 ) 2

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m 2 20 m + 100

( 5 p 12 ) 2

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For the following exercises, factor the polynomials.

x 3 + 216

( x + 6 ) ( x 2 6 x + 36 )

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125 a 3 + 343

( 5 a + 7 ) ( 25 a 2 35 a + 49 )

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64 x 3 −125

( 4 x 5 ) ( 16 x 2 + 20 x + 25 )

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125 r 3 + 1,728 s 3

( 5 r + 12 s ) ( 25 r 2 60 r s + 144 s 2 )

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4 x ( x 1 ) 2 3 + 3 ( x 1 ) 1 3

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3 c ( 2 c + 3 ) 1 4 5 ( 2 c + 3 ) 3 4

( 2 c + 3 ) 1 4 ( −7 c 15 )

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3 t ( 10 t + 3 ) 1 3 + 7 ( 10 t + 3 ) 4 3

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14 x ( x + 2 ) 2 5 + 5 ( x + 2 ) 3 5

( x + 2 ) 2 5 ( 19 x + 10 )

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9 y ( 3 y 13 ) 1 5 2 ( 3 y 13 ) 6 5

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5 z ( 2 z 9 ) 3 2 + 11 ( 2 z 9 ) 1 2

( 2 z 9 ) 3 2 ( 27 z 99 )

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6 d ( 2 d + 3 ) 1 6 + 5 ( 2 d + 3 ) 5 6

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Real-world applications

For the following exercises, consider this scenario:

Charlotte has appointed a chairperson to lead a city beautification project. The first act is to install statues and fountains in one of the city’s parks. The park is a rectangle with an area of 98 x 2 + 105 x 27 m 2 , as shown in the figure below. The length and width of the park are perfect factors of the area.

A rectangle that’s textured to look like a field. The field is labeled: l times w = ninety-eight times x squared plus one hundred five times x minus twenty-seven.

Factor by grouping to find the length and width of the park.

( 14 x −3 ) ( 7 x + 9 )

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A statue is to be placed in the center of the park. The area of the base of the statue is 4 x 2 + 12 x + 9 m 2 . Factor the area to find the lengths of the sides of the statue.

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At the northwest corner of the park, the city is going to install a fountain. The area of the base of the fountain is 9 x 2 25 m 2 . Factor the area to find the lengths of the sides of the fountain.

( 3 x + 5 ) ( 3 x −5 )

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For the following exercise, consider the following scenario:

A school is installing a flagpole in the central plaza. The plaza is a square with side length 100 yd. as shown in the figure below. The flagpole will take up a square plot with area x 2 6 x + 9 yd 2 .

A square that’s textured to look like a field with a missing piece in the shape of a square in the center. The sides of the larger square are labeled: 100 yards. The center square is labeled: Area: x squared minus six times x plus nine.

Find the length of the base of the flagpole by factoring.

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Extensions

For the following exercises, factor the polynomials completely.

16 x 4 200 x 2 + 625

( 2 x + 5 ) 2 ( 2 x 5 ) 2

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16 z 4 2,401 a 4

( 4 z 2 + 49 a 2 ) ( 2 z + 7 a ) ( 2 z 7 a )

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5 x ( 3 x + 2 ) 2 4 + ( 12 x + 8 ) 3 2

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( 32 x 3 + 48 x 2 162 x 243 ) −1

1 ( 4 x + 9 ) ( 4 x −9 ) ( 2 x + 3 )

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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
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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, College algebra. OpenStax CNX. Feb 06, 2015 Download for free at https://legacy.cnx.org/content/col11759/1.3
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