Q1 of 178 Page 551

Find the sum of each of the following APs:

– 37, – 33, – 29, ... to 12 terms.

Here, first term = - 37

Common difference = (-33) - (-37) = 4


Sum of first n terms of an AP is


Sn = [2a + (n - 1)d]


∴ S12 = [2(-37) + (12 - 1)(4)]


= (6)(-74 + 44)


= 6 × (-30)


= - 180


Thus, sum of 12 terms of this AP is - 180.


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