Algebra question I don’t get it because you usually have to multiple A by C but there is no C in the problem.

Ok so basically, when you say multiply A by C, that is simplifying.

And in this case, you are factorising in this question. You turn back into brackets basically.

We have:
72x^2 - 32

x^2 = x squared

factorising means finding the factor of.

(Forget the x squared for the moment to make life easier)

Factors of 72:
1 and 72
2 and 36
3 and 24
4 and 18
6 and 12
8 and 9
(9 and 8 = it repeats so we stop there)

And then factors of 32:
1 and 32
2 and 16
4 and 8
(8 and 4 = repeats so we stop there)

Notice how we see 8 twice in both factors of 72 and 32, this means that we use 8 as the main number we are going to multiply each of the 2 numbers in the brackets by. This is because it is the biggest common factor - this is what we have!

This is what we would have:
8(9-4)

BUT, that is not the answer!
Keep in mind we have the x squared too

But, 32 doesn’t have it?!!

It would be:
8(9x^2 - 4)

Do you get it??

Try to simplify it! Does it equal to 72x^2 - 32?

(And I am so very sorry for the long explanation, once you get the hang of it, it makes sense. Hope my explanation helped) :)