What are the factors of x2+3x-40

(x-5)(x+8)

Let's factor
x
2
+
3
x
−
40
x
2
+
3
x
−
40
The middle number is 3 and the last number is -40.

Factoring means we want something like
(x+_)(x+_)
Which numbers go in the blanks?

We need two numbers that...
Add together to get 3
Multiply together to get -40
Can you think of the two numbers?

Try -5 and 8:
-5+8 = 3
-5*8 = -40

Fill in the blanks in
(x+_)(x+_)
with -5 and 8 to get...
(x-5)(x+8)