http://www.regentsprep.org/regents/math/algtrig/atp2/arithseq.htm [2]
http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html [3]
http://www.mathguide.com/lessons/SequenceArithmetic.html [4]
http://www.purplemath.com/modules/series3.htm [5]
http://www.mathwords.com/a/arithmetic_sequence.htm [6]
http://www.ltcconline.net/greenl/courses/154/seqser/aritmet.htm [7]
Links
[1] https://hootsgo.org/?q=node/6731
[2] http://www.regentsprep.org/regents/math/algtrig/atp2/arithseq.htm
[3] http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html
[4] http://www.mathguide.com/lessons/SequenceArithmetic.html
[5] http://www.purplemath.com/modules/series3.htm
[6] http://www.mathwords.com/a/arithmetic_sequence.htm
[7] http://www.ltcconline.net/greenl/courses/154/seqser/aritmet.htm