Question: Error using dsovle

Please help me out!

there is an error in using dsolve!

Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations

what can I do?

Eq17 := -3*m2*b*(diff(alpha(t), t))^2*(diff(alpha(t), t, t))*(1/2)+((-m2*b*(diff(beta(t), t, t))+2*m3*a*b*sin(beta(t))+b*sin(beta(t))*a*m2+m3*a*c*sin(beta(t)+theta(t)))*(diff(beta(t), t))+(m3*a*c*sin(beta(t)+theta(t))+m3*b*c*sin(theta(t)))*(diff(theta(t), t)))*(diff(alpha(t), t))+(m3*a*b*sin(beta(t))+(1/2)*b*sin(beta(t))*a*m2-(1/2)*m2*b*(diff(alpha(t), t, t))+(1/2)*m3*a*c*sin(beta(t)+theta(t)))*(diff(beta(t), t))^2+(m3*a*c*sin(beta(t)+theta(t))+m3*b*c*sin(theta(t)))*(diff(theta(t), t))*(diff(beta(t), t))+(-m3*b^2-m2*a^2-(1/12)*m2*b^2-m3*a^2-(1/3)*m1*a^2-b*cos(beta(t))*a*m2-m3*b*c*cos(theta(t))-m3*a*c*cos(beta(t)+theta(t))-2*m3*a*b*cos(beta(t))-(1/3)*m3*c^2)*(diff(alpha(t), t, t))+(-m3*b^2-(1/12)*m2*b^2-m3*a*b*cos(beta(t))-(1/3)*m3*c^2-(1/2)*m3*a*c*cos(beta(t)+theta(t))-m3*b*c*cos(theta(t))-(1/2)*b*cos(beta(t))*a*m2)*(diff(beta(t), t, t))+(-(1/3)*m3*c^2-(1/2)*m3*b*c*cos(theta(t))-(1/2)*m3*a*c*cos(beta(t)+theta(t)))*(diff(theta(t), t, t))+((1/2)*m3*a*c*sin(beta(t)+theta(t))+(1/2)*m3*b*c*sin(theta(t)))*(diff(theta(t), t))^2-(1/2)*a*m1*g*cos(alpha(t))-m3*g*((1/2)*c*cos(alpha(t)+beta(t)+theta(t))+a*cos(alpha(t)))-m2*g*((1/2)*b*cos(alpha(t)+beta(t))+a*cos(alpha(t))) = -tau1;

Eq27 := (-m3*a*b*sin(beta(t))-(1/2)*b*sin(beta(t))*a*m2-(1/2)*m2*b*(diff(beta(t), t, t))-(1/2)*m3*a*c*sin(beta(t)+theta(t)))*(diff(alpha(t), t))^2+(-m2*b*(diff(beta(t), t))*(diff(alpha(t), t, t))+m3*b*c*sin(theta(t))*(diff(theta(t), t)))*(diff(alpha(t), t))-3*m2*b*(diff(beta(t), t))^2*(diff(beta(t), t, t))*(1/2)+m3*b*c*sin(theta(t))*(diff(theta(t), t))*(diff(beta(t), t))+(-m3*b^2-(1/12)*m2*b^2-m3*a*b*cos(beta(t))-(1/3)*m3*c^2-(1/2)*m3*a*c*cos(beta(t)+theta(t))-m3*b*c*cos(theta(t))-(1/2)*b*cos(beta(t))*a*m2)*(diff(alpha(t), t, t))+(-m3*b^2-(1/3)*m3*c^2-(1/12)*m2*b^2-m3*b*c*cos(theta(t)))*(diff(beta(t), t, t))+(-(1/3)*m3*c^2-(1/2)*m3*b*c*cos(theta(t)))*(diff(theta(t), t, t))-m3*g*((1/2)*c*cos(alpha(t)+beta(t)+theta(t))+b*cos(beta(t)))+(1/2)*m3*b*c*sin(theta(t))*(diff(theta(t), t))^2-(1/2)*m2*g*b*cos(alpha(t)+beta(t)) = -tau2;

Eq37 := (-(1/2)*m3*a*c*sin(beta(t)+theta(t))-(1/2)*m3*b*c*sin(theta(t)))*(diff(alpha(t), t))^2-m3*b*c*sin(theta(t))*(diff(alpha(t), t))*(diff(beta(t), t))-(1/2)*m3*b*c*sin(theta(t))*(diff(beta(t), t))^2+(-(1/3)*m3*c^2-(1/2)*m3*b*c*cos(theta(t))-(1/2)*m3*a*c*cos(beta(t)+theta(t)))*(diff(alpha(t), t, t))+(-(1/3)*m3*c^2-(1/2)*m3*b*c*cos(theta(t)))*(diff(beta(t), t, t))-(1/3)*m3*c^2*(diff(theta(t), t, t))-k*(theta(t)-f)-(1/2)*m3*g*c*cos(alpha(t)+beta(t)+theta(t)) = -tau3+C*(diff(theta(t), t));

m1 := 1; m2 := 1; m3 := 1; a := 5; b := 5; c := 5; g := 9.81; C := 0; tau1 = 0; tau2 = 0; tau3 = 0; f = 0; k = 0;

ini := alpha(0) = -(1/2)*pi, (D(alpha))(0) = 0, beta(0) = 0, (D(beta))(0) = 0, theta(0) = 0, (D(theta))(0) = 0;

Eq75 := dsolve({E37, ini, Eq17, Eq27}, {alpha(t), beta(t), theta(t)}, numeric, output = listprocedure);