Q. The sum of the first two terms of a GP is -3 and the sum of the first 4 terms is -15. Find the sequence.
A
3, -6, 12, -24
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B
6, -12, 24, - 48
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C
1, 2, 4, 6
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D
3, -15, 75, -375
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E
None of these
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Solution
The correct option is A 3, -6, 12, -24 First term = a Common ratio = r a +ar = -3 a×(1+r+r2+r3)=−15=a(1+r)+ar2(1+r)=−15=a(1+r)(1+r2)=−15=1+r2=5r=±2a=−1forr=2,a=3forr=−2 So possible terms are -1, -2, -4, -8, Or 3, -6, 12, -24