Information about a function
Domain, symmetry, asymptotes, monotonicity, curvature: you already know each of these pieces separately. What sets the EvAU exam exercise apart is that it asks for all of them together, in a fixed order, on a function that may have parameters, be defined piecewise or be given only by its graph. This section brings together the complete procedure and trains it in the contexts where it gets most complicated: rational functions with several asymptotes, exponential and logarithmic functions, and the inverse exercise of reconstructing a graph from its properties.
The complete procedure, step by step
The order is no accident: each step uses information from the previous one (the vertical asymptotes, for example, also split the intervals of monotonicity), so skipping one forces you to repeat work.
Given the rational function $f(x) = \frac{x^2 + 3}{x^2 - 9}$, carry out a preliminary study of its basic elements by determining: a) The domain of the function. b) The…
Given the rational function $f(x) = \frac{x^2 + 3}{x^2 - 9}$, carry out a preliminary study of its basic elements by determining:
- a) The domain of the function.
- b) The points where it crosses the axes of coordinates.
- c) The existence of symmetries (state whether it is even, odd or has no symmetry).
Determine the period of the trigonometric function $f(x) = \sin(2x)$. Next, state with reasons whether the function exhibits any symmetry with respect to the origin or…
Determine the period of the trigonometric function $f(x) = \sin(2x)$. Next, state with reasons whether the function exhibits any symmetry with respect to the origin or the y-axis.
Rational functions: all the asymptotes at once
Rational functions are the case where the most pieces have to be coordinated: they can have several vertical asymptotes (one for each root of the denominator that does not cancel with the numerator) and, in addition, a horizontal or oblique one depending on the degrees.
Given the function $f(x) = \frac{2x}{x-1}$, determine: 1. The equations of its vertical and horizontal asymptotes. 2. The position of the curve with respect to these…
Given the function $f(x) = \frac{2x}{x-1}$, determine:
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The equations of its vertical and horizontal asymptotes.
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The position of the curve with respect to these asymptotes by studying the one-sided limits and limits at infinity.
Given the function $f(x) = \frac{x^2 - 1}{x}$, carry out a study of its infinite branches: a) Check whether it has vertical asymptotes. b) Check whether it has…
Given the function $f(x) = \frac{x^2 - 1}{x}$, carry out a study of its infinite branches:
- a) Check whether it has vertical asymptotes.
- b) Check whether it has horizontal asymptotes.
- c) If it has no horizontal asymptote, find out whether it has an oblique asymptote and find its equation.
Consider the polynomial function $f(x) = \frac{1}{4}x^4 - 2x^2 + 3$. Find the intervals of concavity and convexity, as well as the exact coordinates of its inflection…
Consider the polynomial function $f(x) = \frac{1}{4}x^4 - 2x^2 + 3$. Find the intervals of concavity and convexity, as well as the exact coordinates of its inflection points. Use the symbol $\cup$ to denote the intervals where the function is convex (curving upward) and $\cap$ for the intervals where it is concave (curving downward).
Functions in context: interpreting the asymptote in a real situation
A frequent type of EvAU question puts the function in a context (temperature, population, concentration) and asks you to interpret the horizontal asymptote as the "long-term" value, not just to calculate it.
A team of engineers is monitoring the temperature of an electronic component. The evolution of the temperature $T$ (in degrees Celsius) with respect to time $t$ (in…
A team of engineers is monitoring the temperature of an electronic component. The evolution of the temperature $T$ (in degrees Celsius) with respect to time $t$ (in minutes) is given by the function:
$T(t) = \dfrac{40t + 100}{t + 2}$ with $t \geq 0$
You are asked to:
- a) Find the initial temperature of the component ($t=0$).
- b) Determine the horizontal asymptote of the function and interpret its meaning in the context of the problem (long-term temperature).
Monotonicity and curvature in the complete study
Once the asymptotes are in place, the complete study continues with $f'$ and $f''$ exactly as in the previous section: the stationary points and those excluded from the domain give the intervals of monotonicity; the zeros of $f''$ with a change of sign give the inflection points.
Study the monotonicity (increasing and decreasing intervals) and calculate the relative extrema (maximums and minimums) of the following polynomial function:…
Study the monotonicity (increasing and decreasing intervals) and calculate the relative extrema (maximums and minimums) of the following polynomial function:
$f(x) = x^3 - 3x + 2$
Analyse the curvature of the function $f(x) = x^4 - 6x^2 + 5$. To do this: 1. Find the second derivative $f''(x)$. 2. Determine the intervals of concavity ($\cup$) and…
Analyse the curvature of the function $f(x) = x^4 - 6x^2 + 5$. To do this:
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Find the second derivative $f''(x)$.
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Determine the intervals of concavity ($\cup$) and convexity ($\cap$).
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Find the x-coordinates of the points of inflection.
Carry out a complete study of the monotonicity and relative extrema of the rational function $f(x) = \frac{x^2 - 4x + 4}{x - 1}$. Determine precisely the intervals where…
Carry out a complete study of the monotonicity and relative extrema of the rational function $f(x) = \frac{x^2 - 4x + 4}{x - 1}$. Determine precisely the intervals where the function is increasing and decreasing, as well as the coordinates of its maximums and minimums, if any.
The inverse exercise: from properties to the graph
EvAU also asks the other way round: it gives a list of properties (intercepts, an extremum, limits at infinity) and asks for a sketch that satisfies them all. There is no single correct answer — any curve consistent with the data will do — but you must check each condition one by one.
The following information is known about a function $f(x)$ that is continuous on all of $\mathbb{R}$: It crosses the $X$ axis at $x = -2$ and $x = 2$. It has a relative…
The following information is known about a function $f(x)$ that is continuous on all of $\mathbb{R}$:
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It crosses the $X$ axis at $x = -2$ and $x = 2$.
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It has a relative minimum at $(0, -4)$.
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It is decreasing on $(-\infty, 0)$ and increasing on $(0, +\infty)$.
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$\lim_{x \to +\infty} f(x) = +\infty$ and $\lim_{x \to -\infty} f(x) = +\infty$.
Draw a sketch of the graph that satisfies all these conditions. To help you, here are the axes with the known points; copy the axes onto your paper and draw the curve.
You can do it on paper and send a photo with your answer.
Consider the function $f(x) = \ln(x^2 + k)$, where $k$ is a real parameter. a) Determine the value of $k$ so that the function has a point of inflection at $x = 1$. b)…
Consider the function $f(x) = \ln(x^2 + k)$, where $k$ is a real parameter.
- a) Determine the value of $k$ so that the function has a point of inflection at $x = 1$.
- b) For that value of $k$, study the domain of the function and check whether it exhibits any symmetry (even or odd).
Reading the graph of $f'$: the information in reverse
As in the previous section, an exercise can give only the graph of $f'$ and ask for all the information about $f$: monotonicity, extrema, curvature and inflection points, all at once. The key is not to mix up what $f'$ tells you (rising/falling) with what $f''$ would tell you (curvature of $f$, which is read from the rising and falling of the graph of $f'$ itself).
The following graph corresponds to the derivative function $f'(x)$ of a continuous function $f(x)$ defined on all of $\mathbb{R}$. Using the visual information provided:…
The following graph corresponds to the derivative function $f'(x)$ of a continuous function $f(x)$ defined on all of $\mathbb{R}$. Using the visual information provided:
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State the intervals where the original function $f(x)$ is increasing and decreasing.
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Determine the x-coordinates of the relative extrema of $f(x)$, classifying them as maximums or minimums.
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Study the curvature of $f(x)$ and locate its points of inflection.
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Given that $f(0) = 1$, sketch the graph of the original function $f(x)$, justifying the shape obtained.