1.

Find the sum of first 10 terms of AP 30, 32 , 34 , .

Answer» ONG>Answer:

a=34,

d=32−34=−2

a

N

=10

or, a+(n−1)d=10

or, 34+(n−1)(−2)=10

or, −2(n−1)=−24

or, n−1=12

⇒n=13

∴S

13

=

2

13

[2(34)+12(−2)]

=

2

13

×2[34−12]

=13×22=286.


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