Mister Exam

Limit of the function x-2*y

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The solution

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 lim (x - 2*y)
x->oo         
$$\lim_{x \to \infty}\left(x - 2 y\right)$$
Limit(x - 2*y, x, oo, dir='-')
Detail solution
Let's take the limit
$$\lim_{x \to \infty}\left(x - 2 y\right)$$
Let's divide numerator and denominator by x:
$$\lim_{x \to \infty}\left(x - 2 y\right)$$ =
$$\lim_{x \to \infty}\left(\frac{1 - \frac{2 y}{x}}{\frac{1}{x}}\right)$$
Do Replacement
$$u = \frac{1}{x}$$
then
$$\lim_{x \to \infty}\left(\frac{1 - \frac{2 y}{x}}{\frac{1}{x}}\right) = \lim_{u \to 0^+}\left(\frac{- 2 u y + 1}{u}\right)$$
=
$$\frac{- 0 y + 1}{0} = \infty$$

The final answer:
$$\lim_{x \to \infty}\left(x - 2 y\right) = \infty$$
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
Other limits x→0, -oo, +oo, 1
$$\lim_{x \to \infty}\left(x - 2 y\right) = \infty$$
$$\lim_{x \to 0^-}\left(x - 2 y\right) = - 2 y$$
More at x→0 from the left
$$\lim_{x \to 0^+}\left(x - 2 y\right) = - 2 y$$
More at x→0 from the right
$$\lim_{x \to 1^-}\left(x - 2 y\right) = 1 - 2 y$$
More at x→1 from the left
$$\lim_{x \to 1^+}\left(x - 2 y\right) = 1 - 2 y$$
More at x→1 from the right
$$\lim_{x \to -\infty}\left(x - 2 y\right) = -\infty$$
More at x→-oo
Rapid solution [src]
oo
$$\infty$$