Question

if the first term is 2 and the S5 =one forth of the sum of next 5 term then find the sumof 30 terms?​

Answer 1

a=2

S5=5/2(2*2+4d)

S10=10/2(2*2+9d)

given

S5=1/4(S10-S5)

5/2(4+4d)=5(4+9d)/4

4(1+d)=2(4+9d)/4

2+2d=4+9d/4

7d=-2/4

d=-1/14

,A20=2+19(-1/14)

=2-19/14

=9/14