if the nth term of the AP is (2n+1) find the sum of first n terms of AP
Answers
Answered by
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
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
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
Similar questions