manipulation of symbolic expressions



> From: Mahery Raharinjatovo
> I have a question
> Can maxima solve this equation
> 'diff(x,t,2)+k/m*x=0 ?
> 
> I try with ode2
> 
> (%i1) ode2('diff(x,t,2)+k/m*x=0, x, t);
> but maxima return  this
> "Is  k*m  positive, negative, or zero?"

The solution depends on the sign of k*m.  You need to 
provide this additional information to maxima.

If k>0 and m>0 then you have the first case, a simple harmonic 
oscillator.

(%i1) ode2('diff(x,t,2)+k/m*x=0, x, t);
Is  k m  positive, negative, or zero?

pos;
                              sqrt(k) t            sqrt(k) t
(%o1)             x = %k1 sin(---------) + %k2 cos(---------)
                               sqrt(m)              sqrt(m)

(%i2) ode2('diff(x,t,2)+k/m*x=0, x, t);
Is  k m  positive, negative, or zero?

neg;
                           %i sqrt(k) t           %i sqrt(k) t
                           ------------         - ------------
                             sqrt(m)                sqrt(m)
(%o2)            x = %k1 %e             + %k2 %e

(%i3) ode2('diff(x,t,2)+k/m*x=0, x, t);
Is  k m  positive, negative, or zero?

zero;
(%o3)                           x = %k2 t + %k1

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