OA R-1 R (S,)=A+A(S,) + R+1(1+R)2a /(S,z)=I+/(S,) 2Q(1+R)A-Q/+P A'(S,)=A(T)cos() trial solution I(s, t=I(o)cos(2 2 2 2 2 ' 2 (1 ) ' ' ' ' ' (1 ) ' 1 ' 1 s I Q R A QI P I s A I R R A R A R ∂ ∂ = + − + ∂ ∂ ∂ ∂ + + − + − = ∂ ∂ τ τ ( , ) '( , ) ( , ) '( , ) τ τ τ τ I s I I s A s A A s = + = + ( ) cos( ) ˆ '( , ) ( ) cos( ) ˆ '( , ) l l s I s I s A s A τ τ τ τ = = trial solution: 6