SOLUTION: How to find An and n if Sn,A1 and d is given?

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Question 956360: How to find An and n if Sn,A1 and d is given?
Answer by Edwin McCravy(20056)   (Show Source): You can put this solution on YOUR website!
Start with this sum formula for an arithmetic sequence:



Substitute Sn, a1 and d in this formula
and solve.  It should factor if there is a solution.  

Using the letters and the quadratic formula, I got this:



At least one of those two solutions (using either the + or the -) 
will give a positive whole number for n, if there is a solution.

Then substitute that value of n along with a1 and d
into the general term formula:

  

In some cases there may be two solutions.

Edwin
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