Question

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

Answer 1

Answer:

sum of the first 27 terms = -1431

Step-by-step explanation:

arithmetic series sum of the first n terms formula:

$s_{n} = \frac{n}{2} (2a + (n - 1)d)$

n = 27 terms

first term, a = 25

common difference, d = 19 - 25 = -6

substitute the values into the formula

$s_{27} = \frac{27}{2} (2(25) + (27 - 1)( - 6))$

$s_{27} = 13.5(50 + 26( - 6))$

$s_{27} = 13.5(50 - 156)$

$s_{27} = 13.5( - 106)$

$s_{27} = - 1431$