How do you factor the trinomial x²+8x+15?

2 Answers
Apr 13, 2018

(x+3)(x+5)

Explanation:

First, find the factors of 15.
15=1*15=3*5
Now, split 8x into 2 terms of "x"s containing the numbers 1 and 15 or 3 and 5.
x+15x!=8x, but 3x+5x=8x
Now we have x^2+3x+5x+15.
Next factor x from x^2 and 3x.
x(x+3)
Also factor 5 from 5x and 15.
5(x+3)
We can notice that x(x+3) and 5(x+3) both contain (x+3). Since they both also multiply we can say that the answer is (x+3)(x+5).

Apr 13, 2018

(x+5)(x+3)

Explanation:

Do it backwards to double check.

FOIL

First: x times x is x^2
Outer: x times 3 is 3x
Inner: x times 5 is 5x
Last: 5 times 3 is 15

Add like terms: x^2 + (3x + 5x) + 15

Final answer: x^2 + 8x + 15