In Arithmetic sequence

a13=4;a21=8;a5=?

What will be the answer?? help

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- Feb 7th 2006, 06:00 AMmachiloveArithmetic Sequence
In Arithmetic sequence

a13=4;a21=8;a5=?

What will be the answer?? help - Feb 7th 2006, 07:16 AMCaptainBlackQuote:

Originally Posted by**machilove**

Given that is an arithmetic progression we know that , where is the first term, and

is the common difference.

So:

and:

Subtracting the first of these from the second gives:

, so .

Substituting this value for back into one of the equations gives .

So:

RonL