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...

would you please help me? 

I have a big problem in differentiating with maple! 

here is my equation. 

L := (alpha, beta, theta,alpha(t),beta(t),theta(t))

how can I find diff(L, alpha) ? 

L=(1/2)*I[a]*(diff(alpha(t), t))^2+(1/2)*I[b]*(diff(beta(t), t))^2+(1/2)*I[c]*(diff(theta(t), t))^2+(1/2)*m[3]*(b^2*(diff(beta(t), t))^2+(1/4)*C^2*(diff(theta(t), t))^2+b*c*(diff(beta(t), t...