Q1 of 178 Page 551

Find the sum of each of the following APs:

2, 7, 12, 17, ... to 19 terms.

Here, first term = 2

Common difference = 7 - 2 = 5


Sum of first n terms of an AP is


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


∴ S19 = [2(2) + (19 - 1)5]


= (19)(4 + 90)/2


= (19 × 94)/2


= 893


Thus, sum of 19 terms of this AP is 893.


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