Question

If a = 2 and d = 2, then S15 =
1) 220 2) 230 3) 240 4) 245

give answer step by step!

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Answer 1

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Answer 2

1. Sn= n/2 (a+An)
2. S15= 15/2 (2+S15)
3. S15=15/2(2+30)
4. S15=15/2(32)
5. S15=15×16
6. S15=220