Question

Find a_{4} for the arithmetic series.

S_{4}=-36 and a_{1}=9

Answer 1

use sum formula :

\(\large S_n = \frac{n}{2}(a_1 + a_n)\)

Answer 2

\(\large S_4 = \frac{4}{2}(a_1 + a_4)\)

Answer 3

plugin known given values

Answer 4

\(\large -36 = \frac{4}{2}(9 + a_4)\)

Answer 5

solve \(a_4\)