Q3 of 105 Page 146

In an AP :

given d = 3, a12 = 37 find a and s12

d is the common difference = 3

a is the first term


a12 = 37


a12 = a + (12-1)d


37 = a + (11)3


a = 4


The sum of the series is Sn = [2a + (n-1) d]


S12 = [2×4 + (12-1)×3]


= 6 [41]


= 246


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