1] The sum of 6th and 15th elements of an AP is equal to the sum of space 7th,10th and 12th elements of the same progression.Which element of the series whould be equal to zero?
a]8th b]9th c] 11th d] 13th
solution
(a+5d) + (a+7d) = (a+6d) + (a+9d) + (a+11d)
2a+19d = 3a + 26d
a = -7d
T[8] = a+7d = -7d +7d = 0
a]8th b]9th c] 11th d] 13th
solution
(a+5d) + (a+7d) = (a+6d) + (a+9d) + (a+11d)
2a+19d = 3a + 26d
a = -7d
T[8] = a+7d = -7d +7d = 0
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