How do you find the sum of the arithmetic sequence having the data given $a_{1} = 5$ $a_1= 5$ , $a_{n} = 3$ $a_n = 3$ , n = 20?

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How do you find the sum of the arithmetic sequence having the data given $a_{1} = 5$ $a_1= 5$ , $a_{n} = 3$ $a_n = 3$ , n = 20?

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Answer 1 · 2016-02-06T15:07:56

The information give gives you the first term, the last term and the number of terms. This means we can use the formula $S_{n} = (\frac{n}{2}) (a + t_{n})$ $S_n = (n/2)(a + t_n)$ .

Explanation:

$S_{20} = (\frac{20}{2}) (5 + 3)$ $S_20 = (20/2)(5 + 3)$

$S_{20} = 10 (8)$ $S_20 = 10(8)$

$S_{20} = 80$ $S_20 = 80$

Your sum is 80.

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How do you find the sum of the arithmetic sequence having the data given $a_{1} = 5$ $a_1= 5$ , $a_{n} = 3$ $a_n = 3$ , n = 20?

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How do you find the sum of the arithmetic sequence having the data given a1=5a_1= 5, an=3a_n = 3, n = 20?

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How do you find the sum of the arithmetic sequence having the data given $a_{1} = 5$ $a_1= 5$ , $a_{n} = 3$ $a_n = 3$ , n = 20?