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Cómo despejar an

Sn= (a1 + an)/2 n

User Zpert
by
8.3k points

1 Answer

0 votes

Explanation:

The formula:

=

2

(

1

+

)

S

n

=

2

n

(a

1

+a

n

)

is used to solve for the sum of the arithmetic sequence given the first term a₁, the number of terms n, and the last term in an.

Example:

3, 6, 9, 12, 15,...,123

The first term, a₁ = 3

The last term an = 123

Common difference, d = 3 (because the sequence are multiples of 3)

Number of terms, n= ?

Find the number of terms, n:

an = a₁ + (n-1) (d)

123 = 3 + (n-1) (3)

123 = 3 - 3 + 3n

123/3 = 3n/3

n = 41

To find the sum of the given sequence without adding 3 + 6 + 9, ... + 123, we use the formula:

S₄₁ = (41/2) (3 + 123)

S₄₁ = (41/2) (126)

S₄₁ = (41)(63)

S₄₁ = 2,583 ⇒ the sum of the given sequence

User Linker
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