Progression Practice Test 1

Question : 1 of 23

Marks: +1, -0

The first two terms of a geometric progressionadd up to 12. The sum of the third and thefourth terms is 48. If the terms of thegeometric progression are alternately positiveand negative, then the first term is:

-2
-4
-12
8

Validate

Solution:

According to the question,
GP series is

a, - ar, + ar^2, - ar^3

a - ar = 12 ⇒ a(1 - r) = 12

ar^2 - ar^3 = 48

⇒ ar^2 (1 - r)= 48

Dividing both the equation we get,

r^2 = 4⇒r = 2

Now

a (1 - r) = 12

r = 2

a(1 - 2) = 12 ⇒a = -12

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