Question

find S15 of an AP 1,7,13.....

Answer 1

$hope \: it \: help \: u.$

Answer 2

Answer:

for these a.p.

a=t1=1

d=6

tn=a+(n-1)d

n=15

t15=1+14×6

t15=85

Sn=n/2 (t1+tn)

S15=15/2 ×(1+85)

S15=(15×86)/2

S15=1290/2

S15=645