Mister Exam

Limit of the function e-x

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For end points:

The graph:

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Piecewise:

The solution

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 lim (E - x)
x->oo       
$$\lim_{x \to \infty}\left(e - x\right)$$
Limit(E - x, x, oo, dir='-')
Detail solution
Let's take the limit
$$\lim_{x \to \infty}\left(e - x\right)$$
Let's divide numerator and denominator by x:
$$\lim_{x \to \infty}\left(e - x\right)$$ =
$$\lim_{x \to \infty}\left(\frac{-1 + \frac{e}{x}}{\frac{1}{x}}\right)$$
Do Replacement
$$u = \frac{1}{x}$$
then
$$\lim_{x \to \infty}\left(\frac{-1 + \frac{e}{x}}{\frac{1}{x}}\right) = \lim_{u \to 0^+}\left(\frac{e u - 1}{u}\right)$$
=
$$\frac{-1 + 0 e}{0} = -\infty$$

The final answer:
$$\lim_{x \to \infty}\left(e - x\right) = -\infty$$
Lopital's rule
There is no sense to apply Lopital's rule to this function since there is no indeterminateness of 0/0 or oo/oo type
The graph
Other limits x→0, -oo, +oo, 1
$$\lim_{x \to \infty}\left(e - x\right) = -\infty$$
$$\lim_{x \to 0^-}\left(e - x\right) = e$$
More at x→0 from the left
$$\lim_{x \to 0^+}\left(e - x\right) = e$$
More at x→0 from the right
$$\lim_{x \to 1^-}\left(e - x\right) = -1 + e$$
More at x→1 from the left
$$\lim_{x \to 1^+}\left(e - x\right) = -1 + e$$
More at x→1 from the right
$$\lim_{x \to -\infty}\left(e - x\right) = \infty$$
More at x→-oo
Rapid solution [src]
-oo
$$-\infty$$
The graph
Limit of the function e-x