If the 3rd and 7th term of G.P are 81 and 16 respectively.
Find the first 5th term of the G.P

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Look at the subsequence of b's:

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We use the formula:









The common ratio r for the subsequence is the same
as the common ratio for the original whole sequence.

So we multiply or divide by  as necessary to fill in
the blanks:

To find  we divide  by :



To find  we divide  by :



To find  we multiply  by :

 

To find  we multiply  by :

 

To check we'll go ahead and find 

We can find it either by multiplying  by  
or dividing  by 

If we find a[6] by multiplying  by  

 

If we find a[6] by dividing  by  

 




So it checks.

Answers:

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Edwin