(15) P(-An^2 + Kn + 2Ta) - QTa[e^(ci) + 1] = 0,
(16) -LMn^2 - QT[e^(ci) - 1] = 0,
(17) L[e^(ci) - 1] -Pa[e^(ci) + 1] - 2Qle^(ci) = 0,
leading, on elimination of L, P, Q, to
(2 Ta + Kn - An^2) (1 - Mn^2l/T) - Mn^2
(18) cos c = ---------------------------------------,
2Ta + Kn - An^2 + Mna^2
M n^2 2Ta(a + l) + KNl - An^2l
(19) 2 sin^2 1/2c = -- ----------------------------.
T 2Ta + Kn - An^2 + Mn^2a^2
With K = 0, A = 0, this reduces to Lagrange's condition in the
vibration of a string of beads.