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.
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.
- a) Make a table of values for the first 4 hours ($t=0, 1, 2, 3, 4$).
- b) Draw the graph of the function in that interval.
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 $f(x) = 2x - 3$:
- 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 points obtained.
You can do it on paper and send a photo with your answer.
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 $y = f(x)$.
| $x$ | $-1$ | $0$ | $1$ | $2$ | $3$ |
|---|---|---|---|---|---|
| $y$ | $1$ | $4$ | $7$ | $10$ | $13$ |
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 $f(x) = x^2 - 4$:
- a) Calculate the images for $x = -3, -2, 0, 2, 3$ and organise the results in a table.
- 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.
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 $c$.
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.
- a) What is the initial temperature of the oven?
- b) Construct a table of values for $t = 0, 5, 10, 15$.
- 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.
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 $f(x) = -x^2 + 6x - 5$.
- a) Calculate analytically the coordinates of its vertex and its axis intercepts.
- b) Create a table of values taking two points to the left of the vertex and two to the right.
- c) Draw the graph of the parabola.
You can do it on paper and send a photo with your answer.
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 $B(x) = -300x^2 + 18\,000x - 240\,000$.
- a) Find the break-even points (production for which the profit is zero).
- b) Generate a strategic table of values including the break-even points and the vertex.
- c) How many units must be produced to maximize the profit, and what is this maximum profit?
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 $(2, -1)$.
- a) Set up and solve the system of equations to find the values of $a, b$ and $c$.
- 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.
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.
- 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.
- b) Determine the valid domain of the function $A(x)$ in the context of the problem.
- 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.
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 $\ge 0$.
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 $f(x) = \frac{3x+6}{x-1}$.
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 $f(x) = \sqrt{x+2}$:
- a) Determine its domain analytically.
- b) Complete a table of values for $x \in \{-2, -1, 2, 7\}$ and use it to sketch the graph.
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 $f(x) = \frac{4}{x-2}$:
- a) Determine its domain.
- b) Construct a table of values evaluating the function at points close to $x = 2$ from the left and from the right ($x = 1.9; 1.99; 2.1; 2.01$).
- 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.
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 $f(x) = \sqrt{9-x^2}$.
- a) Calculate its domain of definition analytically.
- b) Make a table of values for $x \in \{-3, -2, 0, 2, 3\}$.
- c) Draw the graph of the function and state its range.
You can do it on paper and send a photo with your answer.
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.
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.
- a) Construct a table of values for the first 4 hours ($t = 0, 1, 2, 3, 4$).
- 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.
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:
- a) Calculate the values of the parameters $M_0$ and $T$.
- 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.
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 $f(x) = \log_2(x+4)$:
- a) Determine analytically its domain and the equation of its vertical asymptote.
- 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.
- c) Plot the graph of the function.
You can do it on paper and send a photo with your answer.
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 $y = x$.
- a) From the highlighted points on the blue curve of $f(x)$, construct a table of values for its inverse function $f^{-1}(x)$.
- b) Draw the graph of the inverse function in your exercise book using symmetry with respect to the line $y=x$.
- c) Write the algebraic expression for $f^{-1}(x)$.
You can do it on paper and send a photo with your answer.
Absolute Value and Piecewise Functions
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 $f(x) = |2x - 5|$:
- 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 function.
You can do it on paper and send a photo with your answer.
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:
$f(x) = \begin{cases} -x + 2 & \text{if } x < 1 \\ 2x - 1 & \text{if } x \ge 1 \end{cases}$
- a) Construct a table of values by evaluating the function at $x = -2; 0; 0.99; 1; 2; 3$.
- 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.
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 $f(x) = |x^2 - 4|$:
- a) Express the piecewise function by removing the absolute value.
- b) Find the axis intercepts.
- 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.
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 $k$:
$f(x) = \begin{cases} x^2 - k & \text{if } x < 2 \\ 2x + 1 & \text{if } x \ge 2 \end{cases}$
- 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).
- 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.
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.
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.
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:
From the graph, determine:
- a) The domain and range of the function.
- b) The value of $f(-2)$ and $f(1)$.
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.
From the graph:
- a) State the initial temperature of the coffee.
- b) What value does the temperature approach as a large amount of time elapses? What physical meaning does the horizontal asymptote have?
- c) Is the function increasing or decreasing? Justify your answer.
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 $f(x) = \frac{ax+b}{cx+d}$:
From the information provided by the graph (asymptotes and axis intercepts):
- a) Determine the domain and range of the function.
- b) Deduce the algebraic expression of the function $f(x)$.
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.