How do indices work?
Starting with multiplication how can we rewrite (click to see):
Did you know the answer? The rule is that when you mutliply two
powers, and the bases are the same, then you add the indices.
If you knew this then good. Now do you know why that is the thing
to do?
Here is a description of why you add the indices


The brackets are needed to show the order of
operations. 


Yet it is still the same result if you leave
the brackets out . 


Just count up the factors. 
Notice that in the first and third lines we used the definition
of indices. In the second line we used the fact that multiplications
can be done in any order whatsoever. Once you know this the "add
the indices" rule follows from the fact that addition is a
short cut way to count up the factors.
We need to know that multiplication can be done in any order because
the order of operation changes when we add the indices. With we only ever multiply by 2, since firstly we do , then , then and so on. With one of the multiplications is . Check out the following expression to see the different
order of operations. Click on a number other than 2 to factorize.
Click on an operation to implement that operation and all the others
that precede it. To get the answer 128 you must click on the operation
that is done last. Which one is the last?
Here is a formal statement of the rule for adding indices.
