Progression (Sequence and Series)Hard

Question

Consider an infinite geometric series with first terma and common ratio r, If its sum is 4 and the second term is 3 /4, then

Options

A.a = 4 / 7, r = 3 / 7
B.a = 2, r = 3 / 8
C.a = 3 / 2, r = 1/ 2
D.a = 3, r =1/ 4

Solution

Since, sum = 4 and second term =
It is given first terma and common ratio r.
⇒       = 4, ar =
⇒      
⇒      
⇒      
⇒       (a - 1)(a - 3) = 0
⇒       a = 1 of 3
When a = 1, r = 3 / 4 and when a = 3, r = 1 / 4
Therefore, (d) is the answer.

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