Question

in 5th and 9th term of arithmetic progression are 44 and 68 respectively calculate the sum of first 25th term​

Answer 1

Step-by-step explanation:

A5=44

a+4d = 44 ____eq.1

A9 =68

a+8d = 68 _____eq.2

subtracting eq.1 from 2-

a+8d-a-4d=68-44

4d=24

d=12

put the value of d in eq.1

a+4×12=44

a+48=44

a=44-48

a=(-4)

a = -4 ,d = 12, n = 25

Sn=n/2(2a+(n-1)d

S25 = 25/2[2×(-4)+(25-1)×12]

S25=25/2[(-8)+24×12]

S25 = 25/2[(-8)+288]

S25 = 25/2×280

S25 =3500