Lesson 9-4
Factoring Trinomials:
ax2 + bx + c
•Factor ax2 + bx + c
F
O
I
L
•(2x + 5)( 3x + 1) = 6x2 + 2x + 15x + 5 - Use the FOIL method
2  15 = 30
6  5 = 30
Observe the following pattern in this product.
6x2 + 2x + 15x + 5
ax2 + mx + nx + c
6x2 + 17x + 5
ax2 + bx + c
2 + 15 = 17 and 2  15 = 6  5
Factors of 30
m + n = b and mn = ac
Sum of Factors
1,30
31
2,15
17
6x2 + 17x + 5 = 6x2 + mx + nx + 5
= 6x2 + 2x + 15x + 5
= (6x2 + 2x) + (15x + 5)
= 2x(3x + 1) + 5(3x + 1)
= (3x + 1) (2x + 5)
Therefore, 6x2 + 17x + 5 = (3x + 1) (2x + 5)
Factor ax2 + bx + c
Factor 7x2 + 22x + 3
Factors of 21
(a  c)
1,21
Sum of Factors
22
Factor ax2 + bx + c
Factor 10x2 - 43x + 28
Factors of 280
(a  c)
-1, -280
-2, -140
-4, -70
-5, -56
-7, -40
-8, -35
Sum of Factors
-281
-142
-74
-61
-47
-43
Factor
• 5x2 + 27x + 10
• 24x2 - 22x + 3
Rule: If the GCF of the terms in a trinomial is an integer
other than 1, you should first factor out this GCF.
Factor
• 3x2 + 24x + 45
Factor
• 4x2 + 24x + 32
Definition
• Prime Polynomial: A polynomial that cannot be
written as a product of two polynomials with integral
coefficients.
Factor 2x2 + 5x -2
Factors of -4
Sum of Factors
1, -4
-3
-1, 4
3
-2, 2
0
There are no factors whose sum is 5. Therefore, 2x2 + 5x -2 cannot be factored
using integers. Thus 2x2 + 5x -2 is a prime polynomial.
Factor
• 3x2 + 7x - 5
Solve by factoring
• Solve. 8a2 - 9a -5 = 4 - 3a.
Solve by factoring
• 18b2 - 19b -8 = 3b2 - 5b
Solve Real-World Problems
At a pep rally, small foam footballs are launched by
cheerleaders using a sling shot. How long is a football in the air
if a student in the stands catches it on its way down 26 feet
above the gym floor. Use the formula h = -16t2 + vt + s, where
h = 26 feet, v = 42, and s = 6. (s is the distance above the
ground when the football is shot.)
h = -16t2 + vt + s
26 = -16t2 + 42t + 6
Solve Real-World Problems
Mrs. Held’s science class built an air-launched model rocket
for competition. When they test-launched their rocket
outside the classroom, the rocket landed in a nearby tree. If
the launch pad was 2 feet above the ground, the initial velocity
of the rocket was 64 feet per second, and the rocket landed
30 feet above the ground, how long was the rocket in flight.
Use the equation h = -16t2 + vt + s.
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Lesson 8-8 - Elgin Local Schools

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