function v = exam8f(t,y,Z,state)
ylag = Z(:,1);
v = zeros(2,1);

gamma = 0.248;
beta  = 1;
A = 0.75;
omega = 1.37;
eta = asin(gamma/A);

v(1) = y(2);
v(2) = sin(y(1)) - state*gamma*cos(y(1)) - beta*ylag(1) ...
       + A*sin(omega*t + eta);