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Secondary 5 · Mathematics
Functions · Real functions

Table and Graph of a Function

A bus charges a fixed fare, and you want to know how much you would pay for several trips. Before using complicated formulas, you need to know how to graph the function: choose values of $x$, calculate their images, and connect the points carefully. The question is: which points should we calculate so we don't miss anything important about the graph? We answer it throughout this page.

Table of Values: Which Points to Choose

A table of values collects pairs $(x, f(x))$ that are then plotted on the coordinate plane. With a linear function, two or three points are enough; with other functions you have to choose more carefully.

Linear Functions and the Difference Table

In a table with equally spaced values of $x$, if the differences between consecutive values of $y$ are constant, the function is linear and that difference is the slope (when $x$ increases by 1). If the differences are not constant but the second differences are, the function is quadratic.

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The cost $C(t)$ in pesos of leaving a car in a parking lot is given by the function $C(t) = 120 + 90t$, where $t$ is the time in hours. a) Make a table of values for the…

The cost $C(t)$ in pesos of leaving a car in a parking lot is given by the function $C(t) = 120 + 90t$, where $t$ is the time in hours.

  1. a) Make a table of values for the first 4 hours ($t=0, 1, 2, 3, 4$).
  2. b) Draw the graph of the function in that interval.
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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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Identify whether the following table of values corresponds to a linear function or a quadratic function by calculating the differences between consecutive values of $y$.…

Identify whether the following table of values corresponds to a linear function or a quadratic function by calculating the differences between consecutive values of $y$. Then, find its algebraic expression $y = f(x)$.

$x$ $-1$ $0$ $1$ $2$ $3$
$y$ $1$ $4$ $7$ $10$ $13$
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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

Parabolas: Vertex and Intercepts

For $f(x)=ax^2+bx+c$, the vertex is at $x_v=-\dfrac{b}{2a}$ and its height is $f(x_v)$. If $a>0$ it opens upward (minimum); if $a<0$, downward (maximum). The intercepts with the $X$-axis come from solving $f(x)=0$, and the intercept with the $y$-axis is $c$.

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The temperature $T$ (in $^\circ\text{C}$) of an industrial oven from when it is turned on is given by the function $T(t) = 20 + 15t$, where $t$ is measured in minutes.…

The temperature $T$ (in $^\circ\text{C}$) of an industrial oven from when it is turned on is given by the function $T(t) = 20 + 15t$, where $t$ is measured in minutes.

  1. a) What is the initial temperature of the oven?
  2. b) Construct a table of values for $t = 0, 5, 10, 15$.
  3. c) How much time must elapse for the oven to reach $200^\circ\text{C}$?

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

Solve
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Consider the quadratic function $f(x) = -x^2 + 6x - 5$. a) Calculate analytically the coordinates of its vertex and its axis intercepts. b) Create a table of values…

Consider the quadratic function $f(x) = -x^2 + 6x - 5$.

  1. a) Calculate analytically the coordinates of its vertex and its axis intercepts.
  2. b) Create a table of values taking two points to the left of the vertex and two to the right.
  3. c) Draw the graph of the parabola.

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

Solve
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The monthly profit $B(x)$, in pesos, of an electronic components factory as a function of the number of units produced $x$ is modeled by the function…

The monthly profit $B(x)$, in pesos, of an electronic components factory as a function of the number of units produced $x$ is modeled by the function $B(x) = -300x^2 + 18\,000x - 240\,000$.

  1. a) Find the break-even points (production for which the profit is zero).
  2. b) Generate a strategic table of values including the break-even points and the vertex.
  3. c) How many units must be produced to maximize the profit, and what is this maximum profit?
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A quadratic function of the form $f(x) = ax^2 + bx + c$ passes through the points $(0, 3)$, $(1, 0)$ and $(2, -1)$. a) Set up and solve the system of equations to find…

A quadratic function of the form $f(x) = ax^2 + bx + c$ passes through the points $(0, 3)$, $(1, 0)$ and $(2, -1)$.

  1. a) Set up and solve the system of equations to find the values of $a, b$ and $c$.
  2. b) Using the algebraic expression obtained, calculate the vertex and construct a table of values to plot the parabola.

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

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It is desired to build a rectangular pen taking advantage of an existing wall for one of its sides. There are $20\text{ m}$ of wire fencing available for the other three…

It is desired to build a rectangular pen taking advantage of an existing wall for one of its sides. There are $20\text{ m}$ of wire fencing available for the other three sides.

  1. a) Express the area $A(x)$ of the pen as a function of the length $x$ of one of the sides perpendicular to the wall.
  2. b) Determine the valid domain of the function $A(x)$ in the context of the problem.
  3. c) Construct a table of values and use it to sketch the graph and find the dimensions that maximise the area.

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

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Rational and Radical Functions: Near the Forbidden

In a rational function, the interesting values are near the value that makes the denominator zero. In a function with a square root, the domain begins where the radicand is zero, and we require radicand $\ge 0$.

Graph of f(x) = 4/(x-2): the left branch drops without bound and the right branch rises without bound as they approach the dashed line x = 2, never crossing the horizontal axis. x = 2 (forbidden) f(x) = 4/(x − 2)
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Calculate analytically the points of intersection with the x-axis and with the y-axis of the rational function $f(x) = \frac{3x+6}{x-1}$.

Calculate analytically the points of intersection with the x-axis and with the y-axis of the rational function $f(x) = \frac{3x+6}{x-1}$.

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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
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Consider the function $f(x) = \sqrt{9-x^2}$. a) Calculate its domain of definition analytically. b) Make a table of values for $x \in \{-3, -2, 0, 2, 3\}$. c) Draw the…

Consider the function $f(x) = \sqrt{9-x^2}$.

  1. a) Calculate its domain of definition analytically.
  2. b) Make a table of values for $x \in \{-3, -2, 0, 2, 3\}$.
  3. c) Draw the graph of the function and state its range.

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

Solve

Exponential and Logarithmic Functions

In an exponential $f(x)=a\cdot b^x$ the values are multiplied by $b$ each time $x$ increases by 1. If $b>1$ it grows very fast; if $0

The logarithmic function $\log_2 x$ requires a positive argument and has a vertical asymptote.

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In a laboratory, the growth of a bacterial population is studied. The number of bacteria $N(t)$ in thousands is given by the function $N(t) = 100 \times 2^t$, where $t$…

In a laboratory, the growth of a bacterial population is studied. The number of bacteria $N(t)$ in thousands is given by the function $N(t) = 100 \times 2^t$, where $t$ is the time in hours.

  1. a) Construct a table of values for the first 4 hours ($t = 0, 1, 2, 3, 4$).
  2. b) Draw the graph of the function. What type of growth is observed?

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

Solve
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The mass $M(t)$ in grams of a radioactive isotope decreases over time $t$ (in days) according to the exponential function $M(t) = M_0 \times (0,5)^{\frac{t}{T}}$, where…

The mass $M(t)$ in grams of a radioactive isotope decreases over time $t$ (in days) according to the exponential function $M(t) = M_0 \times (0,5)^{\frac{t}{T}}$, where $M_0$ is the initial mass and $T$ is the half-life.

Given that at time $t=0$ there were $200\text{ g}$ of substance and after $60\text{ days}$ there are $50\text{ g}$ remaining:

  1. a) Calculate the values of the parameters $M_0$ and $T$.
  2. b) Construct a table of values for $t = 0, 30, 60, 90, 120$ and sketch the graph.

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

Solve
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Given the logarithmic function $f(x) = \log_2(x+4)$: a) Determine analytically its domain and the equation of its vertical asymptote. b) Construct a table of values by…

Given the logarithmic function $f(x) = \log_2(x+4)$:

  1. a) Determine analytically its domain and the equation of its vertical asymptote.
  2. b) Construct a table of values by choosing strategic values of $x$ that result in exact powers of base 2 for the argument of the logarithm.
  3. c) Plot the graph of the function.

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

Solve
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The following figure shows the graph of the exponential function $f(x) = 2^x$ and the line $y = x$. a) From the highlighted points on the blue curve of $f(x)$, construct…

The following figure shows the graph of the exponential function $f(x) = 2^x$ and the line $y = x$.

X Y f(x) y=x
  1. a) From the highlighted points on the blue curve of $f(x)$, construct a table of values for its inverse function $f^{-1}(x)$.
  2. b) Draw the graph of the inverse function in your exercise book using symmetry with respect to the line $y=x$.
  3. c) Write the algebraic expression for $f^{-1}(x)$.

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

Solve

Absolute Value and Piecewise Functions

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Given the modulus function $f(x) = |2x - 5|$: a) Evaluate the function at the points $x = 0; 2; 2.5; 3; 5$ and construct a table of values. b) Draw the graph of the…

Given the modulus function $f(x) = |2x - 5|$:

  1. a) Evaluate the function at the points $x = 0; 2; 2.5; 3; 5$ and construct a table of values.
  2. b) Draw the graph of the function.

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

Solve
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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 absolute value function $f(x) = |x^2 - 4|$: a) Express the piecewise function by removing the absolute value. b) Find the axis intercepts. c) Construct a table…

Given the absolute value function $f(x) = |x^2 - 4|$:

  1. a) Express the piecewise function by removing the absolute value.
  2. b) Find the axis intercepts.
  3. c) Construct a table of values in the interval $[-3, 3]$ and draw its graph.

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: Domain, Range, and Asymptotes

You don't always build the graph: you also have to read it. The domain is the set of $x$ values that have a point on the graph (look at the horizontal axis); the range is the set of $y$ values reached (vertical axis). To find $f(a)$, go up or down from $x=a$ to the curve and read the height.

Graph of a function that gradually approaches a dashed horizontal line as x grows. horizontal asymptote

A cup of coffee cools down: the graph of $T(t)$ goes down and approaches the room temperature without reaching it. That line is the horizontal asymptote, and the function is decreasing.

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Observe the following graph of a function $f(x)$ defined by straight-line segments: From the graph, determine: a) The domain and range of the function. b) The value of…

Observe the following graph of a function $f(x)$ defined by straight-line segments:

X Y 1 4 −2 −4 −1 2 −4 f(x)

From the graph, determine:

  1. a) The domain and range of the function.
  2. b) The value of $f(-2)$ and $f(1)$.
Solve
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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

Back to the beginning: the points to calculate are the intercepts with the axes, the vertex, the values near the forbidden ones, and those on each side of a change of piece.

See all the exercises in this section