Doubt from sequence and series

solved
sequence-series
arithmetic-progression
sum-of-terms
non-constant-ap
easy
pp
#1


Q3 and Q5
My attempt
Q3

Q5

#2


If you have any doubt then ask me

#3

#4

#5

Ques 3

#6

Ques is for a/c not for a/b . So please recheck your ans.

#7

It's in GP so he can surely derive a/c

#8

Ques 5

#9

D will be 5 not -5

#10

As i think it is 5

#11

We have b-a=2(c-b)
If b=ar,c=ar^2 we have after substituting r-1=2r(r-1) \Rightarrow r=\dfrac{1}{2}

Hence \dfrac{a}{c} =4