solving for initial conditions



Dear all,
how can I solve my system, so solve, linsolve,dsolve didn't work ...
Thanks in advance,
alexandre

kill(all);

x:
Xo*%e^(-cita*omega_n*t)*cos(omega_n*(1-cita^2)^(0.5)*t-fio)+X*cos(omega_f*t-fi);
dx: diff(x,t);

eq1: ev(x, t=0)=0;
eq2: ev(dx, t=0)=0;

res: solve([eq1,eq2],[Xo,fio]);


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