T COSa -T COSa,=0 T, sin a2-Tsin a,=(pdx )u 小振动:a→0.a,→>0.cosa;→> 1. cosa,→1 Sm1→> tan a1= OX Sn,2→tana,=l xx+△ T,-T1=0 2x x+dx urx=(pdx utT2 cos2 −T1 cos1 = 0 T T dx ut t sin sin ( ) 2 2 − 1 1 = 小振动: 0, 0,cos 1,cos 1. 1 → 2 → 1 → 2 → x ux x x u = sin 1 → tan1 = 2 2 sin tan x x x u → = + T2 −T1 = 0 T ux x dx Tux x dx ut t ( ) 2 + − 1 =