Properties of Limit at Minus Infinity of Real Function/Difference Rule
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Theorem
Let $a, \alpha, \beta \in \R$.
Let $f, g : \hointl {-\infty} a \to \R$ be real functions such that:
- $\ds \lim_{x \mathop \to -\infty} \map f x$ and $\ds \lim_{x \mathop \to -\infty} \map g x$ exist
where $\ds \lim_{x \mathop \to -\infty}$ denotes the limit at $-\infty$.
Then:
- $\ds \lim_{x \mathop \to -\infty} \paren {\map f x - \map g x}$ exists
with:
- $\ds \lim_{x \mathop \to -\infty} \paren {\map f x - \map g x} = \lim_{x \mathop \to \infty} \map f x - \lim_{x \mathop \to \infty} \map g x$
Proof
This is the combined sum rule with $\alpha = 1$, $\beta = -1$.
$\blacksquare$