1. The problem statement, all variables and given/known data: Two coherent sources emit waves of the same frequency, amplitude and phase. D1 and D2 are the distances of the sources S1 and S2 to point P respectively. How does the amplitude of the resultant wave at P compare with the amplitude of each individual wave when the absolute value of the differences D1 - D2 equals two and half wavelengths? 2. The attempt at a solution: I really don't know how to start. Please help.