Differential equations of second order using ODE45

Hello,

I have to solve to differential equations of second order, which are

2*m*r^2*D2a*(cos(a-2*b)-1)+8*m*r^2*D2b*(2-cos(a-2*b))+sin(a-2*b)*(8*m*r^2*Db*Da-2*m*r^2*Da^2-8*m*r^2*Db^2-2*m*g*r)=0

and

(2*m*r^2*D2a)+(2*m*r^2*D2b)*(cos(a-2*b)-1)+m*g*r*sin(a-2*b)=0

where a and b are variables, m,g and r are constants.

I have been trying to use dsolve but it says no explicit solution can be found.

I am pretty new to matlab and I dont know how to work with ode45...

If anyone could help i'd be really grateful!