WHAT TO DO:
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HOW TO DO IT:
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| 1. Now consider the trinomial with last
sign - Two numbers with a product of
15 and difference of 2 are 5 and 3
|
1. x 2 + 2x - 15 |
| The larger gets the "middle
sign" + Rewriting the terms to factor by grouping:
|
x 2 + 5x - 3x + 15 |
| Then group the terms 2 × 2 into two
terms. Factor common factors. Bring down the middle
sign.
Find the common factor for each group.
Watch the sign of the second group.
|
 |
| Factor out the common factor |
(x + 5)(x - 3) Answer |
| Check by multiplying back
out by FOIL method.
First - Outer - Inner - Last
Note O-I terms.
|
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| 2. Consider the trinomial with last sign
" +" Two numbers with a product of  and sum of  are 
|
 |
| Rewriting the terms to factor by
grouping: Then group the terms 2 × 2 into two terms.
Factor common factors. Bring down the middle sign.
|
 |
| Find the common factor for each group. |
 |
| Factor out the common factor Answer |
 |
| Check by multiplying back out by FOIL
method.
First - Outer - Inner - Last
Note O-I terms.
|
 |
| Consider the trinomial of degree 6 with
middle term degree 3 The last sign is - , two numbers
with a product of 18 and difference of 7 are 9 and 2
|
x 6 - 7x 3 - 18 |
| The larger gets the "middle
sign" " - " |
|
| Rewriting the terms to
factor by grouping: Then group the terms 2 × 2 into
two terms.
Factor common factors. Bring down the middle sign.
Find the common factor for each group.
Watch the sign of the second group.
|
 |
| Factor out the common factor ( x 3 - 9 ) |
Answer (x 3 - 9)(x 3 + 2) |
| Check by multiplying back out by FOIL method.
First - Outer - Inner - Last
Note O - I terms.
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