Question: How to use double angle formula in Maple? (NOT HALF-ANGLE!)

My question is in the title, here is simple example: 


I use formula of abridged multiplication (with help of "factor")


  (sin(a+b) - sin(a-b))(sin(a+b) + sin(a-b))

Then expand:

>expand(%, trig)


And all I whant now is to use double angle formula like this:

4sin(a)cos(b)cos(a)sin(b) = sin(2a)sin(2b)

and keep on working with my double angles! Is it possible? because after few hours of searching I'm not sure.

I'm a beginner, and I have a lot of stupid questions and no one to answer it.

So i hope for you're help:)

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