Sympy exponential equation

[Paul Royik]

Hello.

Why solve(-(21/20)**(12*x) + 120, x) gives empty set?

[Aaron Meurer]

I guess it's just not implemented. I think the solution should be
log(120)/log(S(21)/20)/12. This is related to this issue
https://github.com/sympy/sympy/issues/2999.

Aaron Meurer

On Fri, Jun 5, 2015 at 10:56 AM, Paul Royik <distan...@gmail.com> wrote:
> Hello.
>
> Why solve(-(21/20)**(12*x) + 120, x) gives empty set?
>

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[Paul Royik]

OK.

Thank you.

I just wondered because in sage it is not implemented as well.

[Aaron Meurer]

Ah, it looks like, as with that issue, you can get solve to give you
an answer if you pass check=False:

In [21]: print(solve(-(S(21)/20)**(12*x) + 120, x, check=False))
[-log(120**(1/(-log(7355827511386641) + log(4096000000000000))))]

which looks like the same answer after some log identities are applied
(those large numbers are 21**12 and 20**12, respectively).

Aaron Meurer

[Paul Royik]

Thank you.