Mister Exam

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z^2-i

Limit of the function z^2-i

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The solution

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

The final answer:
$$\lim_{z \to \infty}\left(z^{2} - i\right) = \infty$$
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 z→0, -oo, +oo, 1
$$\lim_{z \to \infty}\left(z^{2} - i\right) = \infty$$
$$\lim_{z \to 0^-}\left(z^{2} - i\right) = - i$$
More at z→0 from the left
$$\lim_{z \to 0^+}\left(z^{2} - i\right) = - i$$
More at z→0 from the right
$$\lim_{z \to 1^-}\left(z^{2} - i\right) = 1 - i$$
More at z→1 from the left
$$\lim_{z \to 1^+}\left(z^{2} - i\right) = 1 - i$$
More at z→1 from the right
$$\lim_{z \to -\infty}\left(z^{2} - i\right) = \infty$$
More at z→-oo
The graph
Limit of the function z^2-i