DSolve[2*q[x]*Sin[y[x]]*Derivative[1][y][x]^2 + Derivative[1][y][x]^3*(Derivative[1][f][x]*Derivative[1][y][x] + f[x]*Derivative[2][y][x]) + Cos[y[x]]*(-(Derivative[1][q][x]*Derivative[1][y][x]) + q[x]*Derivative[2][y][x]) - Derivative[2][y][x]*(Derivative[1][y][x]*Derivative[2][f][x] + 2*Derivative[1][f][x]*Derivative[2][y][x] + f[x]*Derivative[3][y][x]) + Derivative[1][y][x]*(3*Derivative[2][f][x]*Derivative[2][y][x] + Derivative[1][y][x]*Derivative[3][f][x] + 3*Derivative[1][f][x]*Derivative[3][y][x] + f[x]*Derivative[4][y][x]) == 0,y[x],x]