Question 805836: a^2-5a over ab * 3ab over 2
Answer by KMST(5328)   (Show Source):
You can put this solution on YOUR website! 
We can rearrange, and regroup factors,
such as  or  or  or  ,
so we might as well get rid of unnecessary parentheses.
Finally, we can "cancel out" expressions that are common factors of the whole numerator and the whole denominator.
The reason that we can do that is that,
just as we multiplied two rational expressions into a single one,
we can re write it as a product of two factors,
with one of those factors being equal to  .
The whole story is:
You may want to write less steps,
and probably would rather "cancel out" by slashing ans crossing out factors.
That is OK as long as you are crossing out what can be crossed out.
Crossing out without thinking of what it means can lead to nonsense results.
You should not, for example, cross out the that is the exponent of and the that is the denominator and end up with
 because that is not the same.
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