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Rationalize a two-term denominator

When the denominator of a fraction is a sum or difference with square roots, we use the Product of Conjugates pattern to rationalize the denominator.

( a b ) ( a + b ) ( 2 5 ) ( 2 + 5 ) a 2 b 2 2 2 ( 5 ) 2 4 5 −1

When we multiply a binomial that includes a square root by its conjugate, the product has no square roots.

Simplify: 4 4 + 2 .

Solution

.
Multiply the numerator and denominator by the conjugate of the denominator. .
Multiply the conjugates in the denominator. .
Simplify the denominator. .
Simplify the denominator. .
Remove common factors from the numerator and denominator. .
We leave the numerator in factored form to make it easier to look for common factors after we have simplified the denominator.

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Simplify: 2 2 + 3 .

2 ( 2 3 ) 1

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Simplify: 5 5 + 3 .

5 ( 5 3 ) 22

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Simplify: 5 2 3 .

Solution

.
Multiply the numerator and denominator by the conjugate of the denominator. .
Multiply the conjugates in the denominator. .
Simplify the denominator. .
Simplify the denominator. .
Simplify. .

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Simplify: 3 1 5 .

3 ( 1 + 5 ) 4

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Simplify: 2 4 6 .

4 + 6 5

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Simplify: 3 u 6 .

Solution

.
Multiply the numerator and denominator by the conjugate of the denominator. .
Multiply the conjugates in the denominator. .
Simplify the denominator. .

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Simplify: 5 x + 2 .

5 ( x 2 ) x 2

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Simplify: 10 y 3 .

10 ( y + 3 ) y 3

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Simplify: x + 7 x 7 .

Solution

.
Multiply the numerator and denominator by the conjugate of the denominator. .
Multiply the conjugates in the denominator. .
Simplify the denominator. .
We do not square the numerator. In factored form, we can see there are no common factors to remove from the numerator and denominator.

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Simplify: p + 2 p 2 .

( p + 2 ) p 2 2

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Simplify: q 10 q + 10 .

( q 10 ) q 10 2

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Access this online resource for additional instruction and practice with dividing and rationalizing.

Key concepts

  • Quotient Property of Square Roots
    • If a , b are non-negative real numbers and b 0 , then
      a b = a b and a b = a b
  • Simplified Square Roots
    A square root is considered simplified if there are
    • no perfect square factors in the radicand
    • no fractions in the radicand
    • no square roots in the denominator of a fraction

Practice makes perfect

Divide Square Roots

In the following exercises, simplify.

8 x 6 2 x 2 200 m 5 98 m

2 x 2 10 m 2 7

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10 y 3 5 y 108 n 7 243 n 3

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108 p 5 q 2 34 p 3 q 6

6 p q 2

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320 m n 5 45 m 7 n 3

8 n 3 m 3

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Rationalize a One-Term Denominator

In the following exercises, simplify and rationalize the denominator.

Rationalize a Two-Term Denominator

In the following exercises, simplify by rationalizing the denominator.

3 3 + 11 8 1 5

3 ( 3 11 ) −2 −2 ( 1 + 5 )

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4 4 + 7 7 2 6

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5 5 + 6 6 3 7

5 ( 5 6 ) 19 3 ( 3 + 7 )

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6 6 + 5 5 4 11

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3 m 5

3 ( m + 5 ) m 5

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2 x 6

2 ( x + 3 ) x 6

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r + 5 r 5

( r + 5 ) r 5 2

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150 x 2 y 6 6 x 4 y 2

5 y 2 x

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3 5 + 5

3 ( 5 5 ) 20

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2 x 3

2 ( x + 3 ) x 3

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x + 8 x 8

( x + 2 2 ) x 8 2

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Everyday math

A supply kit is dropped from an airplane flying at an altitude of 250 feet. Simplify 250 16 to determine how many seconds it takes for the supply kit to reach the ground.

5 10 4 seconds

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A flare is dropped into the ocean from an airplane flying at an altitude of 1,200 feet. Simplify 1200 16 to determine how many seconds it takes for the flare to reach the ocean.

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Writing exercises


Simplify 27 3 and explain all your steps.
Simplify 27 5 and explain all your steps.
Why are the two methods of simplifying square roots different?

Answers will vary.

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  1. Approximate 1 2 by dividing 1 1.414 using long division without a calculator.
  2. Rationalizing the denominator of 1 2 gives 2 2 . Approximate 2 2 by dividing 1.414 2 using long division without a calculator.
  3. Do you agree that rationalizing the denominator makes calculations easier? Why or why not?
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Self check

After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.

This table has four columns and four rows. The columns are labeled, “I can…,” “confidently.,” “with some help.,” and “no – I don’t get it!” The rows under the column “I can…” read, “divide square roots,” “rationalize a one term denominator.,” and “rationalize a two term denominator.” All the other rows under the columns are empty.

After looking at the checklist, do you think you are well-prepared for the next section? Why or why not?

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
Practice Key Terms 1

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Source:  OpenStax, Elementary algebra. OpenStax CNX. Jan 18, 2017 Download for free at http://cnx.org/content/col12116/1.2
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