factoring perfect square trinomials and the difference of squares
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Factoring Perfect Square Trinomials and the Difference of Squares. Special Products Perfect Square Trinomial. Solve Notice that if you take ½ of the middle number and square it, you get the last number. 6 divided by 2 is 3, and 3 2 is 9. When this happens you have a special product. - PowerPoint PPT PresentationTRANSCRIPT
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Factoring Perfect Square Trinomials and the
Difference of Squares
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Special ProductsPerfect Square Trinomial
Solve
Notice that if you take ½ of the middle number and square it, you get the last number. 6 divided by 2 is 3, and 32 is 9. When this happens you have a special
product. This problem factors into
2 6 9x x
23 3 3x x or x 2
1( )6 32
3 9
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(a + b)² = (a + b)(a + b) = a² +ab + ab + b² = a² +2ab +b²
(a - b)² = (a - b)(a - b) = a² -ab - ab + b² = a² -2ab +b²
a²
Factoring Perfect Square Trinomials
a = 3x b = 5
To factor this trinomial , the grouping method can be used. However, if we recognize that the trinomial is a perfect square trinomial, we can use one of the following patterns to reach a quick solution
2ab b²
For example: (3x + 5)² = (3x)² + 2(3x)(5) + (5)² = 9x² + 30x +25
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Checking for a Perfect Square Trinomial
t² + 10t +25
1. Check if the first and third terms are both perfect squares with positive coefficients.
2. If this is the case, identify a and b, and determine if the middle term equals 2ab
• The first term is a perfect square: t² = (t)²• The third term is a perfect square: 25 = (5)²• The middle term is twice the product of t and
5: 2(t)(5)
t² + 10t +25 Perfect square trinomial
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Checking for a Perfect Square Trinomial
t² + 4t +1
1. Check if the first and third terms are both perfect squares with positive coefficients.
2. If this is the case, identify a and b, and determine if the middle term equals 2ab
• The first term is a perfect square: t² = (t)²• The third term is a perfect square: 1 = (1)²• The middle term is not twice the product of t
and 1: 2(t)(1)
t² + 4t + 1 Is not perfect square trinomial
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Remember: A perfect square trinomial is one that can be factored into two factors that match each other (and hence can be written as the factor squared).
2 12 36x x
This is a perfect square trinomial because it factors into two factors that are the same and the middle term is twice the product of x and 6. It can be written as the factor squared.
26 6 6x x x
Notice that the first and last terms are perfect squares.
The middle term comes from the outers and inners when FOILing. Since they match, it ends up double the product of the first and last term of the factor.
Double the product of x and 6
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25y² - 20y + 4
The GCF is 1.
The first and third terms are positive
The first term is a perfect square: 25y² = (5y)²The third term is a perfect square: 4 = (2)²
The middle term is twice the product of 5y and 2: 20y = 2(5y)(2)
Factor as (5y - 2)²
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Factored Form of a difference of Squares.a² - b² = (a – b)(a + b)
y² - 25
The binomial is a difference of squares.
= (y)² - (5)²
Write in the form: a² - b², where a = y, b = 5.
= (y + 5)(y – 5)Factor as (a + b)(a – b)
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5353 zz
When you see two terms, look for the difference of squares. Is the first term something squared? Is the second term something squared but with a minus sign (the difference)?
259 2 z
22 53 z
The difference of squares factors into conjugate pairs!
difference
rhyme for the day
A conjugate pair is a set of factors that look the same but one has a + and one has a – between the terms.
5353 zz {
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4520 2 y Look for something in common (there is a 5)
945 2 yTwo terms left----is it the difference of squares?
22 325 yYes---so factor into conjugate pairs.
32325 yy
Factor Completely:
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3 2 28 24 18p p q pq Look for something in common There is a 2p in each term
2 22 (4 12 9 )p p pq p Three terms left---try trinomial factoring
"unFOILing"
2 (2 3 )(2 3 )p p q p q
Check by FOILing and then distributing 2p through
2 2
3 2 2
2 (4 12 9 )
8 24 18
p p pq q
p p q pq
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Factoring the Sum and Difference of Cubes and
General Factoring Summary
Factoring a Sum and Difference of Cubes
Sum of Cubes: a³+ b³ = (a + b)(a² -ab +b²)
Difference of Cubes: a³ - b³ = (a - b)(a² +ab +b²)
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= (x + 2) ( (x)² - (x)(2) + (2)²)
x³ + 8 = (x)³ + (2) ³
x³ and 8 are perfect cubes
-(x)(2)
Square the first term of the binomial
Product of terms in the binomial
2x(x + 2)
• The factored form is the product of a binomial and a trinomial.
• The first and third terms in the trinomial are the squares of the terms within the binomial factor.
• Without regard to signs, the middle term in the trinomial is the product of terms in the binomial factor.
Square the last term of the binomial.
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43 s 2943 ss
If it's not the difference of squares, see if it is sum or difference of cubes. Is the first term something cubed (to the third power)? Is the second term something cubed?
6427 3 s
33 43 s
can be sum or difference here
You must just memorize the steps to factor cubes. You should try multiplying them out again to assure yourself that it works.
The first factor comes from what was cubed.
square the first term
sss 12943 2 multiply together but change signsquare the last term
1612943 2 sss
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54 v 21654 vv
What cubed gives the first term?
What cubed gives the second term?
Let's try one more:
12564 3 v
33 54 v
Try to memorize the steps to get the second factor:
First term squared---multiply together & change sign---last term squared
The first factor comes from what was cubed.
square the first term
vvv 201654 2 multiply together but change signsquare the last term
25201654 2 vvv