Hi IVAN,
If dsolve cannot find an explicit solution of a differential equation analytically, then it returns an empty symbolic array. You can solve the differential equation by using MATLAB® numerical solver, such as ode45. For more information, see Solve a Second-Order Differential Equation Numerically.
Also refer to this MATLAB answer: https://www.mathworks.com/matlabcentral/answers/604369-unable-to-find-symbolic-solution-warning
Thanks,
Utkarsh