Progression (Sequence and Series)Hard
Question
The first two terms of a geometric progression add up to 12. The sum of the third and the fourth terms is 48. If the terms of the geometric progression are alternately positive and negative, then the first term is
Options
A.-4
B.-12
C.12
D.4
Solution
Let a, ar, ar2, ....
a + ar = 12 .....(1)
ar2 + ar3 = 48 .....(2)
dividing (2) by (1), we have
⇒ r2 = 4 if r ≠ - 1
∴ r = - 2
also, a = - 12 (using (1)).
a + ar = 12 .....(1)
ar2 + ar3 = 48 .....(2)
dividing (2) by (1), we have
⇒ r2 = 4 if r ≠ - 1
∴ r = - 2
also, a = - 12 (using (1)).
Create a free account to view solution
View Solution FreeMore Progression (Sequence and Series) Questions
The maximum sum of the series 20 + 19 + 18+..... is -...If the ratio of the sum of n terms of two AP′s is 2n : (n + 1), then ratio of their 8th terms is-...If S denotes the sum to infinity and Sn the sum of n terms of the series 1+ + ...., such that S − Sn .< , then ...The sum of the infinite series 12 + 22 x + 32 x2 + ..... is-...Let Then Sn can take value(s)...