Final answer:
Maximum constructive interference requires waves to be exactly in phase, meaning their crests and troughs align, resulting in a wave with twice the amplitude of the individual waves.
Step-by-step explanation:
For maximum constructive interference between two waves, their crests and troughs must align with each other. This means that the crest of one wave should be perfectly aligned with the crest of another wave, and the same is true for the troughs. When this alignment occurs, the waves are said to be exactly in phase. The result of this superposition is that the disturbances add together, producing a new wave with twice the amplitude of the individual waves but with the same wavelength.