When do we put this equation Sn=n/2 ( 2a +(n-1)d) Not this an= a+(n-1)

1.	When do we put this equation Sn=n/2 ( 2a +(n-1)d) Not this an= a+(n-1)d
Answer» We put "Sn= n/2 ( 2a+ ( n - 1 )d )" when we have to find sum of "n" terms of a given AP and we put "an = a + ( n - 1 )d" when we are finding the value of the "n"th term of a given AP.

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