Question

I really need help with multiplying rational expressions. I just can't seem to understand it.
Here is one I need help with:
6a/-1 * 9/-8a^2

Answer 1

\[\frac{ 6a }{ -1} * \frac{ 9 }{ -8a^2 }\]
(easier to read)

Answer 2

There are two ways to approach it

1. Just multiply the numerator and then denominator. Then simplify

6a x 9. 54a
-------- = --------
-1 x -8a^2. 8a^2

Answer 3

We know both 54a and 8a^2 are divisible by 2a
So you can simplify to

27/ 4a

Answer 4

For the second method, you would reduce and then multiply which is helpful for more complicated stuff

Look how 6a and 8a^2 are both divisible by 2a
So
3 9. 27
--- x --- = ----
-1. -4a. 4a

Same answer but less step/work

Answer 5

Okay @nikato, that makes sense. but what about a problem like this:
\[\frac{ -7x }{ 5y } * \frac{ 5x }{ -7 }\]

Answer 6

Same thing. You can use either but I prefer the second becuz it's easier.

Hint: look at diagonal numbers and see what you can simplify

In this problem you have -7x and -7 which are both divisible by -7
And you have 5x and 5y which are both divisible by 5

So
x. x. x^2
-- * --- = -------
y. 1. y