and

On substituting equations(10.91) and(10.92) in equations of motion (10.49)and(10.50), residues of each equations of motion are given by

Using the Galerkin method to minimize the residue, one has

On substituting of equations(10.93) and (10.94)in equations (10.95)and(10.96) the weak formulation can be obtained as

(10.97)

 and

(10.98)

 Equations (10.97)and (10.98)can be written as  

and

with