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

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