Question: How i fix (Error, (in plot) unexpected options)

hi, 

I am a newcomer user(maple16) and am trying to make a graph of energy * time forced oscillation
but I'm having this problem

script:

> restart;

> x := unapply(A*exp(-b*t/(2*m))*cos(`ϖ`*t+phi)
                  +Fmax*cos(psi*t-theta)/sqrt((k-m*psi)^2+b^2*psi^2), t);

> v := unapply(diff(x(t), t), t);

> E := unapply((1/2)*m*v^2+(1/2)*k*x^2, m, v, k, x);

> E2 := subs(v = v(t), x = x(t), phi = arctan(-vo/(xo*omega)),
                theta = arccos[(omega^2-psi^2)/sqrt((omega^2-psi^2)^2+b^2*psi^2)],
                A = sqrt(xo^2+(vo/omega^2)^2), `ϖ` = sqrt(k/m-b^2/(4*m^2)),
                psi = sqrt(k/m-b^2/(2*m^2)), omega = sqrt(k/m), E(m, v, k, x));

> plot(E2, xo = 1, vo = 1, m = 3, k = 2, b = 1, Fmax = 5, t = 0 .. 10);

this give me the error:

error, (in plot) unexpected options: [xo = 1, vo = 1, m = 3, k = 2, b = 1, Fmax = 5, t = 0 .. 10]

can someone help me?

thanks