SOLUTION: find the twentieth term of the arithmetic sequence in which t4 = a and t12=b?

Question 1028709: find the twentieth term of the arithmetic sequence in which t4 = a and t12=b?
Answer by ikleyn(52788) (Show Source): You can put this solution on YOUR website!
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find the twentieth term of the arithmetic sequence in which t4 = a and t12=b?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In other words, find the term    of an AP,  if you are given that
 = a   and   = b.


You have 

 =  = a      and
 =  = b.

Consider   -  =  =   = .

The right side is exactly  .

Therefore,   = 2b - a.

Answer.   = 2b - a.

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