It is the review problem on p.131 of Physics for scientists and engineers ( Serway, 4th edition).
It is the classical problem of 2 blocks in an incline(with angle [itex]\theta[/itex]) with masses 2m and m (in order from bottom to the top of the incline) and 1 block suspended trough a pulley with mass M.
He asks to find M and give the answer as function of m, g, [itex]\theta[/itex].
I got to 2 equations, they are:
I couldn't get to something that wasn't a form of M2+... and it get very strange.
The Attempt at a Solution
It is above.