How do you find the sum of the arithmetic sequence given an = 5, d = -2, n = 12?

Marley Blanchard 2022-09-14 Answered
How do you find the sum of the arithmetic sequence given an = 5, d = -2, n = 12?
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Answers (1)

Bordenauaa
Answered 2022-09-15 Author has 18 answers
We have: an=5 , d=−2 and n=12

By formula:
a n = a 1 + ( n - 1 ) d
5 = a 1 + ( 12 - 1 ) . ( - 2 )
5 = a 1 + 11 . ( - 2 )
5 = a 1 - 22
a 1 = 27

Now,
The formula for sum of an Arithmetic Sequence when the first term a 1 , number of terms n and last term a n are given is:

S u m = ( n 2 ) ( a 1 + a n )

= 12 2 ( 27 + 5 )

= 6 × 32

= 192

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