ClipArt ETC
"Start a trough from A. At the moment of its reflection as a crest a B, start a crest at A as shown. The two crests will meet near the middle of the rope. The crest at the point and moment of meeting results from two forces acting in the same direction; their resultatnt is greater than either of the components." -Avery 1895

Constructive Interference

"Start a trough from A. At the moment of its reflection as a crest a B, start a crest at A as shown.…