Hi Marc, you're not bothering me.

The community sites are here for asking questions.

As a programmer, you will love Mathematica.

To execute my code, simply open a mathematica notebook and paste the code into it.

Press Shift+Enter and you will get the answer (in the form of a rule): {t -> 0.714745}.

Or try this one:

(* Just in case we have stored something in these variables, we clear \

them *)

Clear[f, c, y, t, x];

(* Let Mathematica Solve the Differetial equation y(t).

In case we have more solutions, we use only the first one (with First).

Since we know y(t) and want to get t, we are looking for the inverse \

function of y(t) *)

f[c_, x_] =

InverseFunction[(y /.

First[DSolve[{y[0] == 3/4*Pi, y'[0] == 0, y''[t] == -c*Sin[t]},

y, t]])][x] ;

(* Finally we plot t=f[c,x] *)

Manipulate[

Plot[f[c, x] , {x, -Pi, 2 Pi}, PlotRange -> {{-Pi, 2*Pi}, {-2, 2}},

AxesLabel -> {"x", "t"}],

{{c, 26.48}, -50, 50, Appearance -> "Open"}]

Just play around a bit with mathematica and work through the documentation and tutorials.

It's an incredibly powerful tool.