Solve for x show your work:

x² -6x -72

Question

Solve for x show your work: 

x² -6x -72

luigi0210 · Answer

Well since both numbers have a minus we know it has to be a (x+a)(x-b)

luigi0210 · Answer

In this case the negative number is greater

cwrw238 · Answer

now you need to find 2 numbers whose product is -72
which when added give -6

luigi0210 · Answer

What are all the factors of 72 first of all?

zzr0ck3r · Answer

(x-3)^2 = 72+9

zzr0ck3r · Answer

yet another way^

luigi0210 · Answer

Is that completing the square?

cwrw238 · Answer

yes

luigi0210 · Answer

@Indiadabest do you know how to finish it?

anonymous · Answer

no

luigi0210 · Answer

Come on now, we pretty much numbed it down for you

zzr0ck3r · Answer

x^2 - 6x-72 = x^2 -12x+6x-72
because -12*6 = -72 and -12+6 = -6
so now factor out a x from the pair of terms on the left and a 6 from the ones on the right
x(x-12)+6(x-12)
factor out the x-12
(x-12)(x+6)

luigi0210 · Answer

It's what zz is showing.. I never actually learned that method

zzr0ck3r · Answer

or complete the square
x^2-6x-72 = 0
cut the middle term in half and then do this
(x-3)^2 = 0 + 72 + 9 = 81
(x-3)^2 = 81
(x-3) = -9 and x-3 = 9
x = -12 or x = 6

zzr0ck3r · Answer

the plus 9 on the rhs is making up for the 3 on the left squared

luigi0210 · Answer

And if you prefer you could graph it and see where it intersects the x-axis