Question

can someone solve this question

Answer 1

Sn= 3n+8 / 7n+15

make it into 2 separate parts as there are 2 different ap's :-

find A12 of first ap and then of the other.

first one:-

sn= 3n+8

s(1)= 3+8=11

s(2)= 3(2)+8=14

s(3)= 3(3)+8=17        so AP= 11, 14, 17.....

a=11 , d= 14-11=3

A12= a+(n-1)d

= 11+(12-1)3 = 11+33 = 44.

now a12 of other AP:-

sn=7n+15

s(1)= 22

s(2)= 7(2)+15= 29

s(3)= 21+ 15= 36     so AP= 22,29,36.....

a=22, d=7

A12= a+(n-1)d

= 22+(12-1)7 = 22+77 = 99

so now the ratio, A12 of first AP : A12 of second AP

= 44/99 = 4/9 i.e. 4:9

I HOPE IT IS CORRECT AND HELPS U !!