Question

let S. denotes the sum of n terms of an A.P. If S2n=3Sn
then ratio s3n/sn=

(A) 4
(B) 6
(C) 8
(
10​

Answer 1

Step-by-step explanation:

A/q s2n=3sn

=>2n/2(2*a+(2n-1)d)=3*n/2(2a+(n-1)d)

=>a=d*(n+1)/2

now,

s3n/sn=

3n/2(2*a+(3n-1)d)]/[n/2(2*a+(n-1)d)]

=>3*2[a+(3n-1)d/2] / 2*[a+(n-1)d/2]

=>3*[a+(3n-1)(a/n+1)] / [a+(n-1)(a/n+1)]

=>3*[1+(3n-1)/(n+1)] / [1+(n-1)/(n+1)]

=>3*4n/2n

=>3*2=6(ans)

so , c option is the right answer