Water waves of wavelength 4m are produced by two generators S1 and S2.
Each generation when operated by itself produces waves which have an amplitude A and P which is 3m from S1 and 5m from S2.
When the generator are operated in phase, what is the amplitude of oscillation at P?
A. 0
B.1/2A
C. A
D.2A

»»answer is A. I just need the reasoning :)

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