Answers

2016-07-04T20:43:26+08:00
A1= 3(1) + 5
A1= 8

A12= 3(12) + 5
A12= 36 + 5
A12= 41

Sn= n/2 (A1 +An)
Sn= 12/2 (8 + 41)
Sn= (6)(49)
Sn= 294

The sum of the first 12 terms is 294.
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