Answers

2016-07-03T16:37:33+08:00
Let a3 = a1 and a7 = a5
Using the general term of an arithmetic sequence
8 = -12 + (5-1)d
20 = 4d
d = 5

If you are looking for a1
-12 = a1 + (3-1)5
-12 = a1 + (10)
a1 = -22
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