Question

If the sum of first 8 terms of an AP is 64 and that of its first 15 terms is 225. Find the s of the first n-terms of the A.P.​

Answer 1

Step-by-step explanation:

S

8

=64

S

n

=

2

n

(2a+(n−1)d)

2a+7d=16

S

19

=361

2a+18d=38

Solving, a=1,d=2