Given the arithmetic sequence 8, 5, 2, -1,..., find S20

1 answer:

monitta3 years ago

8 0

The formula to find any term of an an arithmetic sequence is given by
$a _{n}$ = $a _{1}$ =(n-1)d,
where we have first term $a_{1}$ =8,
and d which is the common difference , and n is the term we need to find (in our case is 20)
the difference d=3, as you see each number is the previous minus 3
for S20=8+(20-1)*(-3)=8+(19)*(-3)=8-57=-49
S20=-49, this the 20th term

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