If tn = 3n+1, then Sn =
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Answered by
127
tn=3n+1
Sn-Sn-1=tn
Sn-Sn-1=3n+1
take out the first term
T1=4
second term
T2=7
D=7-4=3
SN=n/2(2×4+(n-1)3)
Sn=n/2(5+3n)
Sn=5n/2+3n^2/2
Sn=(3n^2+5n)/2
Answered by
1
If , then .
Step-by-step explanation:
Here,
Then,
Clearly, and thus the terms are in Arithmetic Progression, whose first term is and common difference is .
Now, the sum of first terms is
Note:
You could also use the following formula to find the required sum:
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