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Sum of n Terms
An AP is a sequence of numbers or terms in which each term except the first one is obtained by adding a fixed number or constant to the term preceding term.
The first term is denoted with ‘a’ and the fixed number is called the common difference denoted by ‘d’.
The common difference is the difference between two successive terms that is t2 – t1 = t3 – t2 = t4 – t3 =….
The sum of first n terms of an AP is given by Sn = 
or 
or
where l = a + (n – 1)d is called the last term.
