# Thread: Null factor Law

1. ## Null factor Law

Factorise and solve:

x^2 + 6x - 72 = 0

2. this is a relatively easy factorization...

(x+12)(x-6)=0

x=-12, 6

Why did you have a problem with it?

3. Just wasn't thinking right. Though don't get me wrong, usually I am not that good at math also. So, I'm prone to mistakes.

4. ## Here is the whole process so you can study it

$x^2+6x-72=0$

We try find the factos adding to 6

$1(-72)=-72$ $-71$
$2(-36)=-72$ $-34$
$3(-24)=-72$ $-21$
$4(-18)=-72$ $-14$
$6(-12)=-72$ $-6$
$12(-6)=-72$ $6$

Now we have to re-write our equation

$x^2+12x-6x-72=0$
$x(x+12)-6(x+12)=0$
$(x-6)(x+12)=0$

Then:
$x-6=0$
$x=6$

or
$x+12=0$
$x=-12$