<Dl> <Dd> 2 + 5 + 8 + 11 + 14 (\ displaystyle 2 + 5 + 8 + 11 + 14) </Dd> </Dl> <Dd> 2 + 5 + 8 + 11 + 14 (\ displaystyle 2 + 5 + 8 + 11 + 14) </Dd> <P> This sum can be found quickly by taking the number n of terms being added (here 5), multiplying by the sum of the first and last number in the progression (here 2 + 14 = 16), and dividing by 2: </P> <Dl> <Dd> n (a 1 + a n) 2 (\ displaystyle (\ frac (n (a_ (1) + a_ (n))) (2))) </Dd> </Dl>

Formula to find the sum of ap series
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