Sum of Arithmetic Sequence/Also presented as

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Sum of Arithmetic Sequence: Also presented as

The Sum of Arithmetic Sequence can also be seen presented in the forms:

\(\ds \sum_{k \mathop = 0}^{n - 1} \paren {a + k d}\) \(=\) \(\ds n a + n \dfrac 1 2 \paren {n - 1} d\)
\(\ds \sum_{k \mathop = 0}^{n - 1} \paren {a + k d}\) \(=\) \(\ds \dfrac 1 2 n \paren {2 a + \paren {n - 1} d}\)


Some present it as:

$\ds \sum_{k \mathop = 0}^n \paren {a + k d} = a \paren {n + 1} + \dfrac 1 2 d n \paren {n + 1}$


The reality is that this is a messy result that cannot be presented elegantly.


Sources