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Multiply (x – 2) (x + 2)…. This product is a little different than the rest. What is it missing? A middle term!
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Warm UpFactor the following.
1) 20x2 - 115x – 30 2) x2 + 4x – 96
3) 14a2 b - 63a5 b6 4) 12x3 +3x2 +20x +5
Factoring-Special Cases
September 4th
So what is a special case? • Multiply (x – 2) (x + 2)….
• This product is a little different than the rest. What is it missing?
• A middle term!
Using what you know…• If given x2 – 4, and asked to factor,
how could you set this up using what you know already?
• What is the middle coefficient, b ?• What is the last number, c ?
• Can you find two numbers that add to be zero and multiply to be – 4 ?
-4
0
Difference of Two Squares
a2 - b2 = (a - b) (a + b)x2 - 22 = (x - 2) (x + 2)x2 – 4 = (x - 2) (x + 2)
This only works for the
DIFFERENCE, not sum/addition!
Example 1Factor x2 - 9 = (a - b) (a + b)
What number squared is 9?
So… (x - 3) (x + 3)
Check your answer by FOIL or box!
Example 2• What if there is a coefficient in the
front?4x2 – 25
It works the same way! What number squared is 4? 25?
(2x - 5) (2x + 5)
You try!1) x2 – 144
2) w2 – 64
3) 16m2 – 49
4) x2 + 25
Another special case…• Multiply (x + 6) (x + 6)….
• What do you notice about the product? Can you find a pattern?
Perfect-Square Trinomials: +
a2 + 2ab + b2 = (a + b) (a + b)
x2 + 8x + 16 = (x + 4) (x + 4)x2 +2(1)(4) + 42 = (x + 4) (x + 4)
If you are having trouble recognizing the pattern,
practice factoring like we did earlier.
Examples1) x2 + 6x + 9
2) x2 + 10x + 25
Perfect-Square Trinomials: -
a2 - 2ab + b2 = (a - b) (a - b) x2 - 14x + 49= (x - 7) (x - 7)x2 – 2(1)(7) + 72 = (x - 7) (x - 7)
Why do we ADD b2?
Examples1) x2 - 10x + 25
2) x2 - 20x + 100
Example • What if there is a coefficient in the
front?4x2 – 12x + 9
What number squared is 4? 9? (2x - 3) (2x - 3)
Why is there a 12x in the middle? Check your answer!
Examples1) 4x2 + 36x + 81
2) 25z2 + 40z + 16
You try!1) 9n2 – 42n + 49
2) 36d2 – 60d + 25
Example• Is 24g2 -6 a difference of two
squares?• What should I do first? • GCF =
• So…. 24g2 – 6 = 6 (4g2 – 1) = 6 (2g - 1) (2g
+ 1)Now factor using difference of squares!
You try!1)27x2 + 90x + 75
2) 8z2 - 64z + 128
Example• Find the side length of the square!
Area = 25r2 - 30r + 9
Factor Completely!!1. 18p2 – 162
2. 50m3 – 98m
Sum of Cubes• a3 + b3 = (a + b)(a2 – ab + b2)
• 27x3 + 1 = (3x)3 + (1)3
= (3x + 1)((3x)2 – (3x)(1) + 12)
= (3x + 1)(9x2 – 3x + 1)
ExamplesExample 1: 8k3 + 729
Example 2: 343u6 + 216
Difference of Cubes• a3 – b3 = (a – b)(a2 + ab + b2)
x3 – 8 = (x)3 - (2)3
= (x – 2) (x2 + (2)(x) + 22) = (x – 2) (x2 + 2x + 4)
ExamplesExample 1: 64x3 – 27
Example 2: 125p3 - 512
So in general…• a3 ± b3 =
(a [same sign] b)(a2 [opposite sign] ab [always positive] b2)
Challenge Question #1Factor: c10 – 30c5d + 225d2
Challenge Question #2If 49x2 – kx + 36 is a perfect square
trinomial, what is the value of k?
Homework• Worksheet
• Start thinking about your test...it’s on TUESDAY!!!