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If the infinite sequence a1, a2, a3, ..., an, ..., each term
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Updated on: 25 Mar 2014, 08:48
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In the infinite sequence \(a_1\), \(a_2\), \(a_3\),...., \(a_n\), each term after the first is equal to twice the previous term. If \(a_5a_2=12\), what is the value of \(a_1\)? A. 4 B. 24/7 C. 2 D. 12/7 E. 6/7 The sequence looks more like x,x^2,x^4,x^8,x^16
a5 = x^16 a2=x^2
x^16x^2 = 12 x^2(x^8 1 ) = 12
I'm lost here. Thanks OPEN DISCUSSION OF THIS QUESTION IS HERE: iftheinfinitesequencea1a2a3aneachterm134617.html
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Originally posted by alimad on 16 May 2008, 03:50.
Last edited by Bunuel on 25 Mar 2014, 08:48, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to PS forum.



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Re: Infinite sequence
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16 May 2008, 05:46
Is it 6/7 ? the seq wil be x , 2x, 4x, 8x...........not x^2,x^4 etc



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Re: Infinite sequence
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16 May 2008, 05:51
alimad wrote: In the infinite sequence, a1,a2,a3,,,,an, each term after the first is equal to twice the previous term. If a5a2 =12, what is the value of a1?
The sequence looks more like x,x^2,x^4,x^8,x^16
a5 = x^16 a2=x^2
x^16x^2 = 12 x^2(x^8 1 ) = 12
I'm lost here. Thanks The sequence is x, 2*x, 2*(2*x), 2*(2*(2*x)) ..... i.e.
nth term = 2^(n1)x
a5=2^4 * x a2=2^2*x
=> a5a2 = (164)x= 12x thus, 12x=12 and the first term x=1



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Re: Infinite sequence
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16 May 2008, 07:17
alimad wrote: In the infinite sequence, a1,a2,a3,,,,an, each term after the first is equal to twice the previous term. If a5a2 =12, what is the value of a1?
The sequence looks more like x,x^2,x^4,x^8,x^16
a5 = x^16 a2=x^2
x^16x^2 = 12 x^2(x^8 1 ) = 12
I'm lost here. Thanks x. 2x. 4x. 8x. 16x. 16x2x=12 14x=12. x=6/7



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Re: Infinite sequence
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16 May 2008, 07:18
anirudhoswal wrote: alimad wrote: In the infinite sequence, a1,a2,a3,,,,an, each term after the first is equal to twice the previous term. If a5a2 =12, what is the value of a1?
The sequence looks more like x,x^2,x^4,x^8,x^16
a5 = x^16 a2=x^2
x^16x^2 = 12 x^2(x^8 1 ) = 12
I'm lost here. Thanks The sequence is x, 2*x, 2*(2*x), 2*(2*(2*x)) ..... i.e.
nth term = 2^(n1)x
a5=2^4 * x a2=2^2*x
=> a5a2 = (164)x= 12x thus, 12x=12 and the first term x=1 This cannot be correct. Just try it. 1, 2, 4, 8, 16. 162 dsnt = 12.



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Re: Infinite sequence
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16 May 2008, 19:00
The OA is 6/7
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Re: In the infinite sequence, a1,a2,a3,,,,an, each term after
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25 Mar 2014, 07:49
a5=2^4*x a2=2^1*x
So a5a2=16x12x=14x 14x=12 => x=6/7



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Re: If the infinite sequence a1, a2, a3, ..., an, ..., each term
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25 Mar 2014, 08:46



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Re: If the infinite sequence a1, a2, a3, ..., an, ..., each term
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30 Aug 2017, 11:27
Process elimination could work as well. Answer 6/7
6/7, 12/7, 24/7, 48/7, 96/7
a5  a2 96/7  12/7 12 Answer is E



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Re: If the infinite sequence a1, a2, a3, ..., an, ..., each term
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02 Sep 2017, 07:08
alimad wrote: In the infinite sequence \(a_1\), \(a_2\), \(a_3\),...., \(a_n\), each term after the first is equal to twice the previous term. If \(a_5a_2=12\), what is the value of \(a_1\)?
A. 4 B. 24/7 C. 2 D. 12/7 E. 6/7 We can let a_1 = x, a_2 = 2x, a_3 = 4x, a_4 = 8x and a_5 = 16x. Thus: 16x  2x = 12 14x = 12 x = 12/14 = 6/7 Answer: E
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Re: If the infinite sequence a1, a2, a3, ..., an, ..., each term &nbs
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