How many terms of the AP. 18,16,14.......... be taken so that their sum is zero
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since n can't be in fraction, then n = 38.
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Explanation: a = 18
d = 16 - 18 = -2
as n is not given use the formula :- Sn = n/2 ( 2a + ( n - 1 ) d )
= 2a + ( n - 1 ) d = 0
= 36 + ( n - 1 ) - 2 = 0
= 36 - 2 ( n - 1 ) = 0
= 36 - 2n - 2 = 0
= 36 = 2n - 2 = 0
= 36 + 2 = 2n
= 38 = 2n
that is,
= 2n = 38
= n = 38/2 = 19
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