27 2 27 22 Tgb Fr2= Ft2tga Ftga F tga 12=7i7 COS B20 1 2 1 d T Ft = Fa = Ft tg    cos t n r t t F t g F = F t g = 2 1 1 1 2 t Fa d T F = = 1 2 2 2 2 t Fa d T F = = Fr1 = Fr2 = Ft2 tg T2 = T1 i