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If the infinite sequence a1, a2, a3, ..., an, ..., each term [#permalink]
16 May 2008, 02:50

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19% (01:49) wrong based on 62 sessions

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_5-a_2=12, what is the value of a_1?

Re: If the infinite sequence a1, a2, a3, ..., an, ..., each term [#permalink]
25 Mar 2014, 07:46

Expert's post

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_5-a_2=12, what is the value of a_1?

A. 4 B. 24/7 C. 2 D. 12/7 E. 6/7

The formula for calculating n_{th} term would be a_n=2^{n-1}*a_1 . So: a_5=2^4*a_1; a_2=2*a_1;