Question

a is 2, d is 8, Sn is 90 then find nAnd An

Answer 1

Sn =
$\frac{n}{2} \times (2a + (n - 1) \times d)$
$90 = (2 \times 2 + (n - 1) \times 8)$
$90 = (4 + 8n - 8)$
$90 = 8n - 4$

n = 12
An =
$a + (n - 1)d$
$2 + (12 - 1) \times 8$
An = 90