Ha sorry:smile:, Heres what iv done.
say y-x=p & z-y=q
hence
d2x/dt2 = d2p/dt2+d2y/dt2,
d2y/dt2 = d2p/dt2+d2x/dt2 = d2q/dt2 + d2z/dt2 &
d2z/dt2= d2q/dt2+d2y/dt2
the original equations then become
d2p/dt2=A(2p-q-Bcos(omega*t))
d2q/dt2=A(2q-p)
but I am then stuck with the same...