Issue with Solve

[j wade]

I am having an odd issue with solve in Sage.  I am using Sage 6.3 in Ubuntu 14.04.

Entering the following commands:

forget()
var('m k c x t')
m=30000
assume(4*k*m-c^2==0)
x=function('x',t)
de = m*diff(x,t,2)+c*diff(x,t)+k*x==0
x=desolve(de,x,ivar=t)
x=x.subs(_K1=0)
x=x.subs(_K2=15)
solve(x(t=(60000/c))==1.5,c)

returns [ ].  Now the last equation clearly has an easy solution; the equation is

900000*e^(-1)/c == 1.50000000000000

If I just enter

solve(900000*e^(-1)/c == 1.50000000000000, c)

I again get [].

But, if I enter

b=var('b')
solve(900000*e^(-1)/b == 1.50000000000000, b)

I get the solution:

[b == 600000*e^(-1)]

Any idea what is going on here?

[Robert Dodier]

On 2015-02-27, j wade <wade....@gmail.com> wrote:

> If I just enter
>
> solve(900000*e^(-1)/c == 1.50000000000000, c)
>
> I again get [].
>
> But, if I enter
>
> b=var('b')
> solve(900000*e^(-1)/b == 1.50000000000000, b)
>
> I get the solution:
>
> [b == 600000*e^(-1)]

For the record, when I try this directly in Maxima, the equation is
solved in both cases. (I assume that Sage calls Maxima to solve
equations; is that right?) Heaven knows Maxima has > 1 bug in which
results depend on the names of variables, but I guess this isn't
one of them.

best,

Robert Dodier