Links
[1] https://www.hootsgo.org/?q=node/6392
[2] http://en.wikipedia.org/wiki/Standing_wave
[3] http://www.physicsclassroom.com/class/waves/Lesson-4/Formation-of-Standing-Waves
[4] http://hyperphysics.phy-astr.gsu.edu/hbase/waves/standw.html
[5] http://physics.info/waves-standing/
[6] http://www.britannica.com/EBchecked/topic/563065/standing-wave