Question

Find the sum of n terms of an ap whose nth term is given by an=5-6n

Answer 1

an = 5 - 6n
a1 = 5 - 6 = a = -1
a2 = 5 - 12 = -7
d = a2-a1 = -7 -(-1) = -6
then
$sn = \frac{n}{2} (2a + (n - 1)d)$