Linear Combination of Indexed Summations
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Theorem
Let $\mathbb A$ be one of the standard number systems $\N,\Z,\Q,\R,\C$.
Let $a,b$ be integers.
Let $\closedint a b$ denote the integer interval between $a$ and $b$.
Let $f, g : \closedint a b \to \mathbb A$ be mappings.
Let $\lambda, \mu \in \mathbb A$.
Let $\lambda \cdot f + \mu \cdot g$ be the sum of the product of $f$ with $\lambda$ and the product of $g$ with $\mu$.
Then we have the equality of indexed summations:
- $\ds \sum_{i \mathop = a}^b \paren {\lambda \cdot \map f i + \mu \cdot \map g i} = \lambda \cdot \sum_{i \mathop = a}^b \map f i + \mu \cdot \sum_{i \mathop = a}^b \map g i$
Proof
We have:
\(\ds \sum_{i \mathop = a}^b \paren {\lambda \cdot \map f i + \mu \cdot \map g i}\) | \(=\) | \(\ds \sum_{i \mathop = a}^b \paren {\lambda \cdot \map f i} + \sum_{i \mathop = a}^b \paren {\mu \cdot \map g i}\) | Indexed Summation of Sum of Mappings | |||||||||||
\(\ds \) | \(=\) | \(\ds \lambda \cdot \sum_{i \mathop = a}^b \map f i + \mu \cdot \sum_{i \mathop = a}^b \map g i\) | Indexed Summation of Multiple of Mapping |
$\blacksquare$