# Thread: factoring help

1. ## factoring help

I need an explanation on how to complete this problem by factoring,
3x^2+17x+20

2. What is the problem ? Anyway, to factorize such equations, you have some methods :
- identity (before any of the following methods, check if your quadratic is not an identity)
- guestimate (try a factorization, expand and check)
- solve & factorize (solve the quadratic by the quadratic formula, and you can easily factorize - yeah I know that perhaps you might be factorizing to solve )
- brainkiller (the most efficient method once you get the grip, quick and easy (see next post of Mattio))

3. First find the factors of 3x, they are x and 3. Now find the factors of 20, they are 1,2,4,5,10, and 20.

Notice it is +20, that means your two binomials that you factor it into will either both be addition or subtraction, but that +17 let's you know it's addition.

Now we have (3x + ?)(x + ?)

Let's test 4 and 5 as multiples of 20.

(3x + 5)(x + 4)

with this you get 3x^2 + 12x + 5x + 20, or 3x^2 + 17x + 20.