Math, asked by dhruvkshatri25, 11 months ago

if the nth term of the AP is (2n+1) find the sum of first n terms of AP

Answers

Answered by shreyajainfeb25
10

Answer:

since,tn=2n+1⇒t1=3 and t2=5

therefore,a=3 and d=t2-t1  =5-3=2

now Sn=n/2(2a+(n-1)d)

=n/2(2(3)+(n-1)(2))

=n/2(6+2n-2)

=n/2(4+2n)

n(n+2)

therefore,Sn=n²+2n

Answered by shashankdesetti
3
Assume n=1
2*1+1=3
Hence a=3
Assume n=2
2*2+1=5
a+d=5
3+d=5
d=2
Now according to question take n=9
a+(n-1)d
3+(9-1)2
3+8*2
3+16=19
Hence sum of first n terms of AP is 19
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