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

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

http://www.purplemath.com/modules/complex.htm

http://www.stewartcalculus.com/data/ESSENTIAL%20CALCULUS/upfiles/topics/ess_at_12_cn_stu.pdf

http://www.mathsisfun.com/numbers/complex-numbers.html

http://www.clarku.edu/~djoyce/complex/

http://algebra.nipissingu.ca/tutorials/complex_numbers.html

http://www.numbertheory.org/book/cha5.pdf

http://www.ping.be/~ping1339/Pcomplex.htm

https://web.math.princeton.edu/~snorin/104/ComplexSolns.pdf

http://www.mathwarehouse.com/algebra/complex-number/

http://www.cimt.plymouth.ac.uk/projects/mepres/alevel/fpure_ch3.pdf

http://www.analyzemath.com/high_school_math/grade_12/complex_numbers.html

http://www.batmath.it/eng/a_complex/test_online/esercizio.htm

http://www.mathsisfun.com/numbers/complex-number-calculator.html

http://crystal.ou.edu/~tprzebin/4103_exam_final_sol.pdf

http://s-mat-pcs.oulu.fi/~ssa/Eka/kaharj.html