I have the expression

1 + Exp[-2 x] (-1 - 2 x (1 + x))

I used Expand to get the x's to multiply within the parentheses, this gives

1 - Exp[-2 x] - 2 Exp[-2 x] x - 2 Exp[-2 x] x^2

I'm expected to get this into the form

1 - Exp[-2 x]*(1 + 2 x + 2 x^2)

I would expect

Collect[1 - Exp[-2 x] - 2 Exp[-2 x] x - 2 Exp[-2 x] x^2, -Exp[-2x]]

to do this but it only returns the expanded form again.


1 Answer 1


Collect[..., -Exp[-2x]] isn't working because some of the terms are -2Exp[-2x] and this doesn't match. If you use Simplify[Collect[Expand[1+Exp[-2x](-1-2x(1+x))], Exp[-2x]]], you should get it in the format you're looking for.

  • $\begingroup$ i feel dumb, maybe a nap is in order before i continue to make such silly mistakes. Thanks for your time. $\endgroup$
    – Kraft Punk
    Oct 6, 2019 at 18:33
  • 2
    $\begingroup$ @KraftPunk I don't think it's a dumb mistake. To a human, it's obvious that we should be able to factor out -Exp[-2x], but sometimes we have to find workarounds when it comes to computers. $\endgroup$
    – MassDefect
    Oct 6, 2019 at 19:36

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