Q1 of 85 Page 104

Find the sum of the first n terms of the following A.P. as asked for:

5, 7, 9, 11, ... upto 30 terms

Formula used.


Sn = [2a + (n–1)d]


d = an + 1–an


In the following A.P


a = 5,


d = a2–a1


= 7–5 = 2;


n = 30


Sn = [2a + (n–1)d]


= [2×5 + (30–1)2]


= 15[10 + 29×2]


= 15[10 + 58]


= 1020


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