You already know how to tell when direct substitution is not enough. Now it is time to turn that catalogue of techniques into reflexes: factorising, rationalising with the conjugate, using the number $e$, replacing a trigonometric expression with its equivalent infinitesimal and, when necessary, comparing which one grows faster.
Before you start, make sure you know: Ruffini's rule (1st Bachillerato)
Factorisation and the conjugate for $\frac{0}{0}$
With quotients of polynomials, the factor $(x-a)$ can always be extracted using Ruffini's rule if $x=a$ makes both numerator and denominator zero. With roots, the conjugate plays the same role.
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Resolve the indeterminate form $\frac{0}{0}$ by simplifying the fraction through factorising the polynomials (you can use algebraic identities or Ruffini's rule):…
Resolve the indeterminate form $\frac{0}{0}$ by simplifying the fraction through factorising the polynomials (you can use algebraic identities or Ruffini's rule):
Calculate the following limit by resolving the indeterminate form $\infty - \infty$ using the conjugate expression: $$\lim_{x \to +\infty} \left( \sqrt{x^2 + 6x} - x…
Calculate the following limit by resolving the indeterminate form $\infty - \infty$ using the conjugate expression:
$$\lim_{x \to +\infty} \left( \sqrt{x^2 + 6x} - x \right)$$
Sketch a graph showing what this result means regarding the distance between the radical function and the line $y = x$.
You can do it on paper and send a photo with your answer.
Equivalent infinitesimals with trigonometric functions
When $x\to0$, some trigonometric functions behave exactly like a much simpler expression. Replacing them with their "equivalent infinitesimal" simplifies limits that would otherwise be very laborious.
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Calculate the limit at $x = 0$ of the following trigonometric expression, using equivalent infinitesimals or known trigonometric identities: $$\lim_{x \to 0} \frac{x…
Calculate the limit at $x = 0$ of the following trigonometric expression, using equivalent infinitesimals or known trigonometric identities:
Based on comparing orders of infinity, determine the value of the following limits without performing complex operations: a) $\lim_{x \to +\infty} \frac{e^x}{x^{10}}$ b)…
Based on comparing orders of infinity, determine the value of the following limits without performing complex operations:
A base that tends to $1$ raised to an exponent that tends to infinity is not automatically equal to $1$: the result depends on the "speed" at which the base approaches $1$.
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Study the behaviour of the function $f(x) = \left( \cos x \right)^{1/x^2}$ as $x$ approaches zero. To do so, calculate: $$\lim_{x \to 0} (\cos x)^{1/x^2}$$ Explain why…
Study the behaviour of the function $f(x) = \left( \cos x \right)^{1/x^2}$ as $x$ approaches zero. To do so, calculate:
$$\lim_{x \to 0} (\cos x)^{1/x^2}$$
Explain why this limit leads to an indeterminate form of the type $1^\infty$ and solve it using natural logarithms or the specific formula for this type of limit.
A multiplayer video game server has detected that the number of active users, $N(t)$, in thousands, follows an exponential growth model as a function of time $t$ (in…
A multiplayer video game server has detected that the number of active users, $N(t)$, in thousands, follows an exponential growth model as a function of time $t$ (in months) defined by the expression:
Calculate the limit of active users as time tends to infinity ($t \to +\infty$). Does the player population stabilise at a finite value or grow indefinitely?
Finding an unknown parameter in a function and classifying the type of discontinuity that remains are the two questions that come up most often, combining everything above.
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Let the function be $g(x) = \dfrac{x^3 - 2x^2 + k}{x^2 - 4}$. a) Calculate the value of $k$ so that the limit of the function as $x \to 2$ is finite. b) Once you have…
Let the function be $g(x) = \dfrac{x^3 - 2x^2 + k}{x^2 - 4}$.
a) Calculate the value of $k$ so that the limit of the function as $x \to 2$ is finite.
b) Once you have found $k$, calculate that limit.
c) Classify the type of discontinuity that the function has at $x = 2$ and at $x = -2$.
Given the rational function depending on a parameter $k \in \mathbb{R}$: $$f(x) = \frac{x^3 - kx^2 + 4}{x-2}$$ Find the value of $k$ so that the limit…
Given the rational function depending on a parameter $k \in \mathbb{R}$:
$$f(x) = \frac{x^3 - kx^2 + 4}{x-2}$$
Find the value of $k$ so that the limit $\lim_{x \to 2} f(x)$ is finite. Once this value is found, calculate the value of the limit.
Comparing infinities and a preview: L'Hôpital's Rule
For $\dfrac{\infty}{\infty}$ with functions (not just sequences), comparing which one dominates still works: powers, exponentials and logarithms have the same order as in sequences.
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Calculate the value of the following limit using the comparison of infinities or L'Hôpital's Rule, analysing in detail the order of magnitude of each term: $$\lim_{x \to…
Calculate the value of the following limit using the comparison of infinities or L'Hôpital's Rule, analysing in detail the order of magnitude of each term:
Calculate the value of the following limits by comparing the orders of magnitude at infinity of the functions involved (exponentials, powers, and logarithms): a)…
Calculate the value of the following limits by comparing the orders of magnitude at infinity of the functions involved (exponentials, powers, and logarithms):
a) $\lim_{x \to +\infty} \frac{\ln(x^{10} + 5)}{x}$
b) $\lim_{x \to +\infty} \frac{3^x}{x^2 + 100x}$
c) $\lim_{x \to +\infty} \frac{e^x + x^5}{2e^x - \sqrt{x}}$