Q. 1 B3.7( 3 Votes )
Find the sum of the first n terms of the following A.P. as asked for:
5, 7, 9, 11, ... upto 30 terms
Answer :
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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