Question

if 5th term of an as is 23 find sum of its first n terms

Please answer fast please ​

Answer 1

Step-by-step explanation:

nth term tn=a+(n−1)d

a= First term

d= Common difference

n= number of terms

tn=nth term

Given 

T5+T9=30

a+4d+a+8d=30

2a+12d=30

a+6d=15

a=−6d+15

now

T25=3T8

a+24d=3(a+7d)

24d−21d=3a−a

3d=2a

3d=2(6d−15)

15d=30

d=2

a=15−6×2