Im new to mathematica and I'm having some problems with a system of differential equations.
I am trying to describe a double pendulum by two 2nd order differential equations, q1'' and q2'', but I don't seem to get the same solution as other people.
I've attached my try, and below are two links with the solution, I can't seem to get.
Note: I'm not talking about solving the differential equations, I'm just talking about "isolating" q1'' and q2''.
Lastly, sorry for my bad english.
Attachment: double pendulum tried solution.nb, URL: ,