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Question
Determine the sum of first 100 terms of given A.P. 12, 14, 16, 18, 20, ......
Activity :- Here, a = 12, d = `square`, n = 100, S100 = ?
Sn = `"n"/2 [square + ("n" - 1)"d"]`
S100 = `square/2 [24 + (100 - 1)"d"]`
= `50(24 + square)`
= `square`
= `square`
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Solution
Here, a = 12, d = 14 - 12 = 2, n = 100, S100 = ?
Sn = `"n"/2 [2"a" + ("n" - 1)"d"]`
S100 = `100/2 [24 + (100 - 1)"d"]`
= 50[24 + 99(2)]
= 50(24 + 198)
= 50(222)
= 11100
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