http://iitg.vlab.co.in/?sub=59&brch=166&sim=618&cnt=1
https://engineering.purdue.edu/~bouman/ece301/notes/pdf/SysProp.pdf
http://users.ece.gatech.edu/~bonnie/book/worked_problems.html
http://www.niceindia.com/qbank/it1201_signals_and_systems__.pdf
http://faemino.ucsd.edu/~soniamartinez/teaching/143a_SignalsSystems/data/analog-systems.pdf
http://assets.cambridge.org/97805218/49661/excerpt/9780521849661_excerpt.pdf
http://maxim.ece.illinois.edu/teaching/fall08/lec3.pdf
http://www.le.ac.uk/eg/mct6/teaching/eg1110/lect2_4.pdf
http://en.wikibooks.org/wiki/Signals_and_Systems/Time_Domain_Analysis
http://web.eecs.umich.edu/~fessler/course/451/l/pdf/c2.pdf
http://www.ece.jhu.edu/~cooper/courses/214/signalsandsystemsnotes.pdf
http://www3.nd.edu/~mhaenggi/ee344-04/overview.html
http://www.le.ac.uk/eg/mct6/teaching/eg1110/intro_lect_4.pdf
http://www.eas.uccs.edu/wickert/ece2610/lecture_notes/LTIPropertiesExample_solved.pdf