Q1 of 85 Page 104

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

1, 1.5, 2, 2.5, 3, ... upto 16 terms

Formula used.


Sn = [2a + (n–1)d]


d = an + 1–an


In the following A.P


a = 1,


d = a2–a1


= 1.5–1 = 0.5;


n = 16


Sn = [2a + (n–1)d]


= [2×1 + (16–1)0.5]


= 8[2 + 15×0.5]


= 8[2 + 7.5]


= 76


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