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98. What is the sum of the first 27 terms in the arithmetic series 25 +19+13 + ...?​

98 What Is The Sum Of The First 27 Terms In The Arithmetic Series 25 1913 class=

Sagot :

Answer:

sum of the first 27 terms = -1431

Step-by-step explanation:

arithmetic series sum of the first n terms formula:

[tex] s_{n} = \frac{n}{2} (2a + (n - 1)d)[/tex]

n = 27 terms

first term, a = 25

common difference, d = 19 - 25 = -6

substitute the values into the formula

[tex] s_{27} = \frac{27}{2} (2(25) + (27 - 1)( - 6))[/tex]

[tex] s_{27} = 13.5(50 + 26( - 6))[/tex]

[tex] s_{27} = 13.5(50 - 156)[/tex]

[tex] s_{27} = 13.5( - 106)[/tex]

[tex]s_{27} = - 1431[/tex]