Question

if for an A.P.S51 = 7650, Find the 26th term.

Answer 1

let first term a and common difference d of AP
use formula ,
Sn=n /2 {2a+(n-1) d}

7650=51/2 {2a+(51-1) d}

15300/51=2a+50d

300=2 {a+25d}

150=a+25d---------------(1)

now nth term of AP=a+(n-1) d
so, 26th term=a+(26-1) d
=a+25d=150 { from (1)

Answer 2

s51=51/2(2a+50d)
7650=51/2(2a+50d)
7650=51(a+25d)
150=a+25d
a+d=6
so,a=6-d
t26=a+25d
=6-d+25d
6+24d
24d=-6
d=1/4
a=6-1/4
24-1/4
a=23/4
t26=n/2(2a+(n-1)d
=13(1/2+25*1/4)