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Find the sum of first seven terms of 5+11+17......​

1 Answer

7 votes

Explanation:

d = a2 - a1

d = 11 - 5

d = 6


Sn \: = (n)/(2) (2a1 + (n - 1)d) \\ S7 = (7)/(2) (2 * 11 + (7 - 1)6) \\ S7 = (7)/(2) (22 + 36) \\ S7 = (7)/(2) * 58 \\ S7 = 7 * 29 \\ S7 = 203

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