How to factor Quadratic Equations
and using the Zero Product Property
Factoring Quadratic Equations x2+bx+c
Factor x2-12x-28
To factor x2-12x-28 you must find factors of -28 that will have a sum of -12
x2-12x-28=(x+m)(x+n)=x2+(m+n)x+mn
mn=-28
m+n=-12
| Factors of -28(mn) | Sum(m+n) |
| -1,28 | 27 |
| 1,-28 | -27 |
| -2,14 | 12 |
| 2,-14 | -12 |
| -4,7 | 3 | 4,-7 | -3 |
I would use a 2x2 chart to help solve these kind of equations
On the top right and side of box 1 would be the factors of a
On the top left of box 2 and the side of box 3 would be the factors of c
This is just like a chart so you should just multiply 2x and 3 then 1 and x

then

Then the one on the side should make an equation like this: 2x+1 and the top x+3
then there is your factor
2x2+7x+3=(2x+1)(x+3)
note
If the factoring chart doesn't work,
then I suggest you switch the numbers
around, but only one side
If that doesn't work try other numbers
or your equation is not factorable!
Zero Product Property
Let A and B be real numbers or algebraic expressions. If AB=0, then A=0 and B=0
Same from last example
x2-12x-28=(x+2)(x-14)=0
Separate the two factored answers as if they were equations
So it would be like this x+2=0 and x-14=0 and you want to solve for x
x=-2 or x=14 and that would be the answer
Practice
Factor
1. x2+5x+4
2. x2+13x+40
3. 3k2+32k-11
4.18n2+9n-14
Solve
5.x2-3x-4=0
6.5x2-13x+6=0