Answer:
constructive interference in which waves strengthen each other
Explanation:
Some definitions:
- Costructive interference occurs when two (or more) waves meet each other in phase, so with same displacement at the same point. In such situation, the two waves strengthen each other, and the amplitude of the resultant wave is the sum of the amplitudes of the individual waves
- Destructive interference occurs when two waves meet each other in anti-phase, so with opposite displacement at the same point. In such situation, the two waves cancel each other out, and the amplitude of the resultant wave is the difference of the amplitudes of the individual waves (which means zero if the two waves are identical)
For light waves interfering with each other, 'white' means costructive interference, while 'black' means destructive interference (because black is absence of colors, so this means that the waves cancel each other out). In this problem, we see that point X, Y and X are white, therefore they are point of constructive interference, where the waves strengthen each other.
