how to solve 3 dimensional nonlinear equations? plz help me i am new to matlab

how to solve these system of equations? i have solved the system of ordinary differential equation using dsolve ,but i am not getting how to move further ? *??? Error using ==> mupadmex Error in MuPAD command: dsolve cannot use variable D

Error in ==> sym.sym>sym.mupadmexnout at 2003 out = mupadmex(fcn,args{:});

Error in ==> dsolve>mupadDsolve at 190 [var_list,R] = mupadmexnout('mllib::dsolve',sys,x,ignoreConstraints);

Error in ==> dsolve at 97 [R,vars] = mupadDsolve(ignoreConstraints,varargin{1:narg});*

these are errors obtained while solving:::: >> syms thetap thetag theta t Ip Ig I rp rg k1 k2 kw cw s Tfp Tp Tfg T

>> [thetap,thetag,theta]=dsolve('Ip*D2theta+rp*(k1+k2)*s+Tfp=Tp','Ig*D2theta-rg*(ki+k2)*s+cw*D(theta-thetag)+kw*(theta-thetag)-Tfg=0','I*D2theta-cw*D(theta-thetag)-kw*(theta-thetag)=-T','t')