if an =2n+1 then s2 is
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Answered by
1
Answer:
S2=12
Step-by-step explanation:
S2=12if an =2n+1 then s2 is
Answered by
0
Answer:
S-- 12
Step-by-step explanation:
Given a
n
=2n
2
+1 (1)
Put n=1 in (1), we get,
a
1
=2(1)
2
+1
∴a
1
=2+1
∴a
1
=3
Put n=2 in (1), we get,
a
2
=2(2)
2
+1
a
2
=2(4)+1
∴a
2
=9
Thus, d=a
2
−a
1
∴d=9−3
∴d=6
Now, sum of n terms of A.P. is,
S
n
=
2
n
[2a+(n−1)d]
Put n=2 in above equation, we get,
S
2
=
2
2
[2a+(2−1)d]
∴S
2
=1[(2×3)+(1×6)]
∴S
2
=1[6+6]
S=12
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