How do you factor trinomials?

Here is an example of one: x2 - 8x - 20

Question

How do you factor trinomials?

Here is an example of one: x2 - 8x - 20

anonymous · Answer

http://ts4.mm.bing.net/th?id=HN.608013394737893209&w=257&h=179&c=7&rs=1&pid=1.7 You want me to walk you through it?

jumperman · Answer

Please.

precal · Answer

@nelsonjedi FOIL is used to expand (x+a)(a+b) out not to factor

jumperman · Answer

2 and 8?

jumperman · Answer

Well how do you factor?

precal · Answer

take the last term 20

precal · Answer

list all the factors of 20

precal · Answer

1 times 20
2 times 10
4 times 5

anonymous · Answer

My bad.

precal · Answer

@nelsonjedi no problem

precal · Answer

the minus sign in front of 20  ie -20 tells you to subtract the factors

anonymous · Answer

I use FOIL as an example and then tell them to work backwards

jumperman · Answer

So 1, 2, 4, 5, 10, and 20 are all the factors?

precal · Answer

20-1 =19
10-2=8
5-4=1  
use the ones that will give you positive numbers
so don't use 1-20 =-19   we don't care about the signs at this point, we do the signs separately

precal · Answer

we are looking for the middle term which is 8
so which factors do we use?

jumperman · Answer

10-2.

precal · Answer

by the way if the middle term is not listed then the trinomial is what is known as "prime" and can not be factored but in this case we can find 8

precal · Answer

ok so let's break it up

precal · Answer

|dw:1405004053287:dw|x times x is x to the second power, agreed?

jumperman · Answer

Yes.

precal · Answer

|dw:1405004098929:dw|2 times 10 will give you 20