A partial sum of an arithmetic sequence is given. Find the sum. 1 + 5 + 9 + · ·

nicekikah

nicekikah

Answered question

2021-09-26

A partial sum of an arithmetic sequence is given. Find the sum. 1 + 5 + 9 + · · · + 401

Answer & Explanation

tabuordy

tabuordy

Skilled2021-09-27Added 90 answers

Find the common difference d by subtracting two consecutive terms
5-1 So, d=4
Find n by using the nth term formula.
an=a1+(n1)d
401=1+(n1)(4)
401=1+4n4
401=4n3
4n=404
n=101
Now we can find the sum of arithmetic sequence
Sn=n(a1+an2)
Sn=101(1+4012)
Sn=101(4022)
Sn=101(201)
Sn=20301
Result: Sn=20301

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