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Functions · Real functions

Table and graph of a function

Before analysing a function with analytical tools, you need to know how to sketch it: choose the values of $x$ carefully, calculate their images and join the points sensibly, knowing which regions need more points than others.

Before you start, make sure you know: Second-degree polynomial. Parabolas (4th ESO)
Before you start, make sure you know: Piecewise-defined functions (4th ESO)

Table of values: which points to choose

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Given the linear function $f(x) = 2x - 3$: a) Complete a table of values for $x \in \{-2, 0, 1, 3\}$. b) Draw the graph of the function in the Cartesian plane using the…

Given the linear function $f(x) = 2x - 3$:

  1. a) Complete a table of values for $x \in \{-2, 0, 1, 3\}$.
  2. b) Draw the graph of the function in the Cartesian plane using the points obtained.

You can do it on paper and send a photo with your answer.

Solve
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Consider the quadratic function $f(x) = x^2 - 4$: a) Calculate the images for $x = -3, -2, 0, 2, 3$ and organise the results in a table. b) Draw the graph of the…

Consider the quadratic function $f(x) = x^2 - 4$:

  1. a) Calculate the images for $x = -3, -2, 0, 2, 3$ and organise the results in a table.
  2. b) Draw the graph of the function and identify the coordinates of its vertex.

You can do it on paper and send a photo with your answer.

Solve

Rational and radical functions: points near the excluded value

In a rational function, the interesting values are near the value that makes the denominator zero, not far from it; in a radical function, the domain starts exactly where the radicand becomes zero.

Graph of a function with a vertical asymptote at x = 2, showing how the branches move apart towards plus and minus infinity near the excluded value. x = 2 (excluded)
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Given the radical function $f(x) = \sqrt{x+2}$: a) Determine its domain analytically. b) Complete a table of values for $x \in \{-2, -1, 2, 7\}$ and use it to sketch the…

Given the radical function $f(x) = \sqrt{x+2}$:

  1. a) Determine its domain analytically.
  2. b) Complete a table of values for $x \in \{-2, -1, 2, 7\}$ and use it to sketch the graph.
Solve
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Given the rational function $f(x) = \frac{4}{x-2}$: a) Determine its domain. b) Construct a table of values evaluating the function at points close to $x = 2$ from the…

Given the rational function $f(x) = \frac{4}{x-2}$:

  1. a) Determine its domain.
  2. b) Construct a table of values evaluating the function at points close to $x = 2$ from the left and from the right ($x = 1,9; 1,99; 2,1; 2,01$).
  3. c) Based on the results obtained, what graphical feature does the function display at $x = 2$?

You can do it on paper and send a photo with your answer.

Solve

Piecewise functions: continuity at the junction

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Given the piecewise function: $f(x) = \begin{cases} -x + 2 & \text{if } x < 1 \\ 2x - 1 & \text{if } x \ge 1 \end{cases}$ a) Construct a table of values by evaluating…

Given the piecewise function:

$f(x) = \begin{cases} -x + 2 & \text{if } x < 1 \\ 2x - 1 & \text{if } x \ge 1 \end{cases}$

  1. a) Construct a table of values by evaluating the function at $x = -2; 0; 0,99; 1; 2; 3$.
  2. b) Draw the graph of the function and state whether it is continuous at $x = 1$.

You can do it on paper and send a photo with your answer.

Solve
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Given the piecewise function depending on a parameter $k$: $f(x) = \begin{cases} x^2 - k & \text{if } x < 2 \\ 2x + 1 & \text{if } x \ge 2 \end{cases}$ a) Find the value…

Given the piecewise function depending on a parameter $k$:

$f(x) = \begin{cases} x^2 - k & \text{if } x < 2 \\ 2x + 1 & \text{if } x \ge 2 \end{cases}$

  1. a) Find the value of $k$ so that the two branches of the function "connect" at the point $x = 2$ (that is, so that the function is continuous).
  2. b) Using the value of $k$ found, construct a table of values in the interval $[0, 4]$ and sketch the graph of the function.

You can do it on paper and send a photo with your answer.

Solve

Reading a graph: trends and asymptotes

You do not always construct the graph: you also have to read it when it is already drawn, extracting information without needing the formula.

Graph of a function that gradually approaches a dashed horizontal line as x increases towards infinity. horizontal asymptote
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The following graph shows the evolution of the temperature $T$ (in $^\circ\text{C}$) of a cup of coffee as a function of time $t$ (in minutes) since it is served. From…

The following graph shows the evolution of the temperature $T$ (in $^\circ\text{C}$) of a cup of coffee as a function of time $t$ (in minutes) since it is served.

90 20 t (min) T (°C) Ambient temperature

From the graph:

  1. a) State the initial temperature of the coffee.
  2. b) What value does the temperature approach as a large amount of time elapses? What physical meaning does the horizontal asymptote have?
  3. c) Is the function increasing or decreasing? Justify your answer.
Solve
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Observe the following graph of a rational function of the form $f(x) = \frac{ax+b}{cx+d}$: From the information provided by the graph (asymptotes and axis intercepts):…

Observe the following graph of a rational function of the form $f(x) = \frac{ax+b}{cx+d}$:

X Y x=3 y=2 2 4/3

From the information provided by the graph (asymptotes and axis intercepts):

  1. a) Determine the domain and range of the function.
  2. b) Deduce the algebraic expression of the function $f(x)$.
Solve

Summary

See all the exercises in this section