SOLUTION: The second, fourth and eight terms of an A.p from the first three consecutive terms of a G.P. the sum of the third and fifth terms of the A.p is equal to 20. Find the (a) first 4

Question 1110258: The second, fourth and eight terms of an A.p from the first three consecutive terms of a G.P. the sum of the third and fifth terms of the A.p is equal to 20. Find the (a) first 4 terms of the A.p
(b) sum of the first 10 terms of the A.p.
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
The second, fourth and eight terms of an A.p form the first three consecutive terms of a G.P. the sum of the third and fifth terms of the A.p is equal to 20. Find the (a) first 4 terms of the A.p
(b) sum of the first 10 terms of the A.p.
The second fourth and eighth terms can be written as
a+d , a+3d,a+7d
They are in GP

therefore a=d
as per second condition and a=d
a+2d +a+4d =20
8d =20
d=5/2 but d=a
First four terms are
t1=5/2
t2=5/2 +5/2 = 5
t3 = 5 + 5/2 = 15/2
t4 = 15/2 + 5/2 = 10

you can calculate S10

t8 = a+7d = 5/2 + 7(5/2) = 20

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