Maths help!

Dunks

Dunks

Dunks

Soldato
Joined
31 Oct 2004
Posts
8,703
Location
London
Hey guys, currently having a mild bit of confusion, all is explained in the image below!

XYumHl.jpg


Having difficulty understanding why 3! changes to 4!. This is taken from the solutions, it also seems to change to '12' which is neither 3! or 4!.

I'm thinking it must just be an epic mistake in the solutions, anyone care to prove me wrong? :p
 
Forgot to mention that sin^3 (w t) = 1/4 (3sin(w t) - sin3(w t))

It's something to do with the 1/4 but I still can't see it :(
 
Yeah figured it out, I get to this:

(-A^3 / 3!) * (1/4) which gives me (-A^3 / 24) and 24 = 4!.

Now to see why it changes to 12 further down the line :p
 
i wish my equations looked that nice for my signal processing assignment :(
(actually, to be fair, they do look that nice to start with, then mid way through working them out you end up with a hideous equation that takes two lines of paper to write down)
 
Dunks said:
(-A^3 / 3!) * (1/4) which gives me (-A^3 / 24) and 24 = 4!.
Click to expand...

That's a very convoluted way of thinking about that, and suggests you haven't grasped what 4! actually means.

4! = 4*3*2*1

3! = 3*2*1

n! = n*(n-1)*....3*2*1 (for n >=5, obviously, you pedants)

So 4*3! is obviously 4!, you don't need to mess about working out 24 is 4!
 
They use exclamation marks in maths now?

The stuff in the OP makes my head explode!
 
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