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# Sum of Arithmetic Sequence

The sum of $$n$$ terms in an arithmetic progression can be obtained by taking the number of terms being added $$n$$, multiplying by the sum of the first and last number in the sum, and then dividing by 2:

$\frac{n(a_1 + a_n)}{2}.$

For example:

$1+4 +7+10+13 = \frac{5(1 + 13)}{2} = \frac{5 \times 14}{2} = 35.$

Note by Arron Kau
2 years, 5 months ago