Question = Simplify a4 x a5-------------------------------------------So here we have two 'groups' of a being multiplied together. We can rewrite a4 and a5 as the following:a4 = a x a x a x aa5 = a x a x a x a x aIf we substitute these into the original question we have:a4 x a5 = a x a x a x a x a x a x a x a x aIf we count these we have 9 lots of a multiplied together, so this can be rewritten as a9.Notice that 4 + 5 = 9, so when we multiply two identical values or letters (these are sometimes called "variables") that are presented in index / power form, we can simply add the powers together.So, to conclude: a4x a5 = a9, which we can obtain from the techniques of multiplying indices.