How do you find the sum of the arithmetic sequence given a1 = 7, d = - 3, n = 20?

Kallie Fritz

Kallie Fritz

Answered question

2022-09-21

How do you find the sum of the arithmetic sequence given a1 = 7, d = - 3, n = 20?

Answer & Explanation

Katelyn Chapman

Katelyn Chapman

Beginner2022-09-22Added 13 answers

The formula for the sum of an arithmetic sequence when a, d and n are given is:

S u m = ( n 2 ) [ 2 a + ( n - 1 ) d ]

Here : a 1 = 7 , d = - 3 and n = 20

= ( 20 2 ) [ 2 . 7 + ( 20 - 1 ) . - 3 ]
= 10 . [ 14 + 19 . ( - 3 ) ]
= 10 . [ 14 - 57 ]
= 10 . ( - 43 )
= - 430

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