Answer:
When multiple sine waves interact and they are in phase with one another, this is known as constructive interference and results in a significant increase in amplitude.
Step-by-step explanation:
When two waves enter in constructive interference (assuming both waves have the same amplitude), their amplitude increases twice as much as when they were separated. In other words, the amplitude of the resulting wave is equal to the sum of each separated wave.
This can be easily appreciated in the graphic below.