A'(s,D=A(Tcos( A I'(s, t)=l(T)cos( (S,τ (S,)=A+A(S,) (S,)=1+/(S,t)7 ( ) cos( ) ˆ '( , ) ( ) cos( ) ˆ '( , ) l l s I s I s A s A τ τ τ τ = = A I s s A I I’(s,τ) ( , ) '( , ) ( , ) '( , ) τ τ τ τ I s I I s A s A A s = + = +