http://en.wikipedia.org/wiki/Wave_equation

http://mathworld.wolfram.com/WaveEquation.html

http://hyperphysics.phy-astr.gsu.edu/hbase/waves/wavsol.html

http://homepage.ntu.edu.tw/~twhsheu/course/Finite%20difference/NUMER2+3.pdf

http://www.math.ubc.ca/~feldman/m267/separation.pdf

http://www.iitr.ac.in/outreach/web/CIRCIS/UG/FSV/Wave%20Equation%20in%20Fluids.pdf

http://www.iitk.ac.in/math/faculty/malayb/Uniqeness_Thms.pdf

http://www.mathtube.org/sites/default/files/lecture-notes/Lamoureux_Michael.pdf

http://www.math.psu.edu/wysocki/M412/Notes412_6.pdf

http://www.cartage.org.lb/en/themes/sciences/physics/acoustics/SoundWaves/wavequation/Examples/Examples.htm

http://people.maths.ox.ac.uk/trefethen/pdectb/wave1d2.pdf

http://ramanujan.math.trinity.edu/rdaileda/teach/s12/m3357/lectures/lecture_3_1_short.pdf

http://www.math.hmc.edu/~ajb/PCMI/Lecture7print.pdf

http://www.physnet.org/modules/pdf_modules/m201.pdf

http://www.physics.usu.edu/riffe/3750/lecture_notes.htm

http://people.uncw.edu/hermanr/phy335/SampeProblems.pdf

http://www-rohan.sdsu.edu/~rcarrete/teaching/M-636/assignments/exam2.pdf