Then

P (−An2 + Kn + 2Ta) − QTa (eci + 1) = 0,

(15)

−LMn2 − QT (eci − 1) = 0,

(16)

L (eci − 1) − Pa (eci + 1) − 2Qleci = 0,

(17)

leading, on elimination of L, P, Q, to

cos c = (2 Ta + Kn − An2) (1 − Mn2l/T) − Mna2,
2Ta + Kn − An2 + Mna2

(18)