1. The problem statement, all variables and given/known data 0 = A+B+D 0 = A-B+C 0 = A exp(k) + B exp(-k) + C sin(k) + D cos(k) 0 = A exp(k) - B exp(-k) + C cos(k) - D sin(k) Solve for A, B, C, D in the above system. (k is a positive real number) 2. Relevant equations N/A 3. The attempt at a solution 1st equation=> D = -A-B 2nd equation=> C = B-A Put these into the 3rd and 4th equation, we get: 0 = A exp(k) + B exp(-k) + (B-A) sin(k) + (-A-B) cos(k) 0 = A exp(k) - B exp(-k) + (B-A) cos(k) - (-A-B) sin(k) How should I continue?? Just wondering: In a system of 4 equations in 4 unknowns, is it POSSIBLE to have infinitely many solutions? or must the solution be unique? Any help is greatly appreciated!