Re: finding inverses of functions
- To: mathgroup at smc.vnet.net
- Subject: [mg126426] Re: finding inverses of functions
- From: Peter Breitfeld <phbrf at t-online.de>
- Date: Thu, 10 May 2012 04:55:41 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <jod7lu$5f8$1@smc.vnet.net>
John Accardi wrote:
> Hello, I am trying to get Mathematica to find the inverse of:
>
> y = 3x^3 + 2e^(2x) (which I know is invertible)
>
> InverseFunction only seems to give inverses of built-ins, like Sine.
>
> I tried:
>
> Solve[ y == 3x^3 + 2e^(2x), x ] but get a message that Solve does not have methods suitable. (Solve works for simpler functions, however.)
>
> Any ideas? Thanks.
>
Because your function is trancendental you can't hope for a closed form.
But InverseFunction can be used:
f[x_] = 3 x^3 + E^(2 x)
g[y_] = InverseFunction[f][y]
Plot[f[x], {x, -2, 3}]
Plot[g[y], {y, -50, 250}]
--
_________________________________________________________________
Peter Breitfeld | Bad Saulgau, Germany | http://www.pBreitfeld.de