Question: Maple can't solve it....wolframalpha does

Hi, i got this diff ecuation to answer. It is an ecuation of a proyectile, it give the angle of speed with respect to time. I typed it on wolfram; got an aswer. When i tried on maple without any initial condition, got a good answer. With an initial condition, didn't get nothing. I even tried with the interactive solver, got a 'can't solve'. So this is my ecuation:

dx/dt = -[g cos(x)] / [vo - g t sin(x)]

I had to find the initial coindition for myself after that, i supect what the problem is. Maple gave an aswer in terms of arctan (y,x), and i think, based on my own try, it doesn't know how to find a term if it's inside the arctan function, typed in that way. So i rewrited it like arctan (y/x), anf found my constant C1.

Another problem i got was about this system of diff ecuations:

dx/dt = (-k/m) (x srqt(x^2 + y^2))

dy/dt = (-k/m) (y srqt(x^2 + y^2))

Again was wolfram who gave me a good answer to the problem. So you are going to understand im thinking wolfram is better on symbolic calculation. Thanks anyway for your help and effort.