Is there a greatest common factor between all of the terms in the given expression? If so, you should factor that out first.
(r-5)(r+8)
Practice makes perfect
To factor a trinomial with a leading coefficient of 1, think of the process as multiplying two binomials in reverse. Let's start by taking a look at the constant term.
r^2+3r-40
In this case, we have -40. This is a negative number, so for the product of the constant terms in the factors to be negative, these constants must have the opposite sign (one positive and one negative.)
Factor Constants
Product of Constants
1 and - 40
- 40
-1 and 40
- 40
2 and -20
-40
-2 and 20
- 40
4 and -10
-40
-4 and 10
- 40
5 and -8
-40
-5 and 8
- 40
Next, let's consider the coefficient of the linear term.
r^2+3r-40
For this term, we need the sum of the factors that produced the constant term to equal the coefficient of the linear term, 3.
Factors
Sum of Factors
1 and - 40
- 39
-1 and 40
39
2 and - 20
-18
-2 and 20
18
4 and -10
-6
-4 and 10
6
5 and -8
-3
-5 and 8
3
We found the factors whose product is - 40 and whose sum is 3.
r^2+3r-40 ⇔ (r-5)(r+8)
Checking Our Answer
Check your answer ✓
We can check our answer by applying the Distributive Property and comparing the result with the given expression.
After applying the Distributive Property and simplifying, the result is the same as the given expression. Therefore, we can be sure our solution is correct!
