Complete Destructive Interference Steps:

• Superposition principle states waves add amplitudes at each point.
• For zero resultant, amplitudes must cancel exactly, requiring equal magnitudes and 180° phase difference.
• Same amplitude and frequency ensure consistent interference pattern.
• At the instant shown, check phase shift between waves in each diagram.

Why A is correct:

• Waves in A are inverted (180° out of phase), so crests align with troughs, causing total cancellation per superposition.

Why the others are wrong:

• B: Waves in phase (0° shift), so amplitudes add constructively to double amplitude.
• C: Partial phase shift (e.g., 90°), results in non-zero net amplitude.
• D: Phase difference less than 180° (e.g., 120°), leads to partial interference, not zero.

Final answer: A