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x-x^4

Limit of the function x-x^4

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     /     4\
 lim \x - x /
x->oo        
$$\lim_{x \to \infty}\left(- x^{4} + x\right)$$
Limit(x - x^4, x, oo, dir='-')
Detail solution
Let's take the limit
$$\lim_{x \to \infty}\left(- x^{4} + x\right)$$
Let's divide numerator and denominator by x^4:
$$\lim_{x \to \infty}\left(- x^{4} + x\right)$$ =
$$\lim_{x \to \infty}\left(\frac{-1 + \frac{1}{x^{3}}}{\frac{1}{x^{4}}}\right)$$
Do Replacement
$$u = \frac{1}{x}$$
then
$$\lim_{x \to \infty}\left(\frac{-1 + \frac{1}{x^{3}}}{\frac{1}{x^{4}}}\right) = \lim_{u \to 0^+}\left(\frac{u^{3} - 1}{u^{4}}\right)$$
=
$$\frac{-1 + 0^{3}}{0} = -\infty$$

The final answer:
$$\lim_{x \to \infty}\left(- x^{4} + x\right) = -\infty$$
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
Rapid solution [src]
-oo
$$-\infty$$
Other limits x→0, -oo, +oo, 1
$$\lim_{x \to \infty}\left(- x^{4} + x\right) = -\infty$$
$$\lim_{x \to 0^-}\left(- x^{4} + x\right) = 0$$
More at x→0 from the left
$$\lim_{x \to 0^+}\left(- x^{4} + x\right) = 0$$
More at x→0 from the right
$$\lim_{x \to 1^-}\left(- x^{4} + x\right) = 0$$
More at x→1 from the left
$$\lim_{x \to 1^+}\left(- x^{4} + x\right) = 0$$
More at x→1 from the right
$$\lim_{x \to -\infty}\left(- x^{4} + x\right) = -\infty$$
More at x→-oo
The graph
Limit of the function x-x^4