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Algebra 1 · Mathematics
Functions · Functions

Representing Functions

Mateo rents an electric scooter. The app says "$\$1$ to unlock, plus $\$0.25$ per minute." The sign at the dock shows the same prices as a table, and the company's report shows them as a graph. Are those three different things, or one? Spoiler: one function, three ways to look at it. Moving smoothly between formula, table, and graph is the skill of this page, and we will use it on every function family you meet in Algebra 1.

From a table to a graph

Before you make a table, find the domain: the $x$-values where the formula actually works. A graph can only exist there.

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Find the domain of the radical function $f(x) = \sqrt{2x - 8}$.

Find the domain of the radical function $f(x) = \sqrt{2x - 8}$.

Solve
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The period of oscillation $T$ (in seconds) of a simple pendulum depends on its length $L$ (in feet) according to the radical function $T(L) = 2\pi\sqrt{\frac{L}{9,8}}$.…

The period of oscillation $T$ (in seconds) of a simple pendulum depends on its length $L$ (in feet) according to the radical function $T(L) = 2\pi\sqrt{\frac{L}{9,8}}$. Calculate the domain of the function in this context and determine the period of a pendulum of $2,45$ feet in length.

Solve

Lines: from a story or a graph

Graph of the scooter cost: a line starting at (0, 1) that rises 1 dollar for every 4 minutes 0 4 8 12 1 2 3 4 run: 4 min rise: 1 dollar minutes cost (dollars) (0, 1)
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A taxi driver charges an initial fee of $\$3$ and $\$1,5$ for each mile traveled. Write the algebraic expression of the function that relates the cost of the trip to the…

A taxi driver charges an initial fee of $\$3$ and $\$1,5$ for each mile traveled. Write the algebraic expression of the function that relates the cost of the trip to the miles traveled.

Solve
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Observe the graph of the line and determine its slope, its y-intercept, and its algebraic expression.

Observe the graph of the line and determine its slope, its y-intercept, and its algebraic expression.

X Y
Solve

Parabolas: vertex and translations

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Determine the coordinates of the vertex and the equation of the axis of symmetry of the parabola $f(x) = x^2 - 6x + 5$.

Determine the coordinates of the vertex and the equation of the axis of symmetry of the parabola $f(x) = x^2 - 6x + 5$.

Solve
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From the parent parabola $y = x^2$ (dashed line), a translation was applied to obtain the parabola drawn with a solid line. Write the equation of the new parabola and…

From the parent parabola $y = x^2$ (dashed line), a translation was applied to obtain the parabola drawn with a solid line. Write the equation of the new parabola and state the translation vector applied.

X Y V(4, 3)
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Parabolas in real life: maximum and minimum

When a problem asks for the greatest or least value of something that follows a quadratic, you are being asked for the vertex. The $x$-coordinate tells you when or how many, and the $y$-coordinate tells you how much.

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The profit of a technology company, in thousands of dollars, is given by the function $B(x) = -2x^2 + 120x - 1000$, where $x$ is the number of devices sold in hundreds.…

The profit of a technology company, in thousands of dollars, is given by the function $B(x) = -2x^2 + 120x - 1000$, where $x$ is the number of devices sold in hundreds. How many devices must they sell to maximize their profit and what is this maximum profit?

Solve
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A farmer has $120$ feet of fencing to enclose a rectangular plot of land adjacent to a straight river. Knowing that he does not need to fence the side along the river,…

A farmer has $120$ feet of fencing to enclose a rectangular plot of land adjacent to a straight river. Knowing that he does not need to fence the side along the river, write the function that gives the area of the plot in terms of the width $x$ perpendicular to the river. What dimensions maximize the area and what is the maximum area?

Solve

Rational functions: $\dfrac{a}{x-h} + k$

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State the vertical and horizontal asymptotes of the inverse proportion function $f(x) = \frac{2}{x-3} + 4$.

State the vertical and horizontal asymptotes of the inverse proportion function $f(x) = \frac{2}{x-3} + 4$.

Solve
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Renting a charter bus for a school trip costs $\$600$. Write the function $C(x)$ that determines the cost per student as a function of the number of students $x…

Renting a charter bus for a school trip costs $\$600$. Write the function $C(x)$ that determines the cost per student as a function of the number of students $x$ attending. If at the last minute $5$ students drop out, write the new cost per student function and find how much each will pay if originally $30$ students were going to go.

Solve
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Given the inverse proportion function $f(x) = \frac{3x - 1}{x + 2}$, find the expression for its inverse function $f^{-1}(x)$. Prove algebraically that the vertical and…

Given the inverse proportion function $f(x) = \frac{3x - 1}{x + 2}$, find the expression for its inverse function $f^{-1}(x)$. Prove algebraically that the vertical and horizontal asymptotes are swapped between $f(x)$ and $f^{-1}(x)$.

Solve

Exponential functions

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A bacteria culture doubles every hour. If initially there are $100$ bacteria, write the exponential function $N(t)$ that gives the number of bacteria as a function of…

A bacteria culture doubles every hour. If initially there are $100$ bacteria, write the exponential function $N(t)$ that gives the number of bacteria as a function of time $t$ in hours.

Solve
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$\$5000$ is invested in a bank account that offers an annual compound interest rate of $4\%…

$\$5000$ is invested in a bank account that offers an annual compound interest rate of $4\%$. Write the exponential function that models the accumulated balance after $t$ years and calculate the balance after $5$ years.

Solve
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The amount of Carbon-14 in a fossil decreases exponentially according to the function $N(t) = N_0 \cdot (0,5)^{\frac{t}{5730}}$, where $N_0$ is the initial amount and…

The amount of Carbon-14 in a fossil decreases exponentially according to the function $N(t) = N_0 \cdot (0,5)^{\frac{t}{5730}}$, where $N_0$ is the initial amount and $t$ is the time in years. If a bone retains only $12,5\%$ of its original Carbon-14, how many years have passed?

Solve

Logarithmic functions

Since $b^y$ is never zero or negative, a logarithm can only be taken of a positive number. The function $f(x) = \log_b x$ is the inverse of $b^x$: swapping $x$ and $y$ reflects the graph across the line $y = x$.

Graphs of y equals 2 to the x and y equals log base 2 of x, mirror images across the line y equals x y = 2ˣ y = log₂(x) y = x (0, 1) (1, 0) mirror images across y = x
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Determine the domain of the logarithmic function $f(x) = \log_3(x - 5)$.

Determine the domain of the logarithmic function $f(x) = \log_3(x - 5)$.

Solve
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The sound intensity level $L$, in decibels (dB), is calculated using the logarithmic function $L(I) = 10 \log_{10} \left( \frac{I}{I_0} \right)$, where $I$ is the sound…

The sound intensity level $L$, in decibels (dB), is calculated using the logarithmic function $L(I) = 10 \log_{10} \left( \frac{I}{I_0} \right)$, where $I$ is the sound intensity and $I_0 = 10^{-12} \text{ W/m}^2$ is the threshold of hearing. Calculate the sound intensity level of a normal conversation whose intensity is $I = 10^{-6} \text{ W/m}^2$.

Solve

Piecewise functions

Graph of parking cost: flat 6 dollars up to 2 hours, then rising 3 dollars per hour until 5 hours, then flat at 15 dollars 0 2 5 8 6 15 flat rate daily max hours cost (dollars) 3 dollars per hour
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Given the piecewise function $f(x) = \begin{cases} 2x+1 & \text{if } x < 0 \\ x^2 & \text{if } x \ge 0 \end{cases}$, evaluate $f(-2)$, $f(0)$, and $f(3)$.

Given the piecewise function $f(x) = \begin{cases} 2x+1 & \text{if } x < 0 \\ x^2 & \text{if } x \ge 0 \end{cases}$, evaluate $f(-2)$, $f(0)$, and $f(3)$.

Solve
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The following graph shows the speed of a cyclist as a function of time. Determine the algebraic expression of the piecewise function that represents it.

The following graph shows the speed of a cyclist as a function of time. Determine the algebraic expression of the piecewise function that represents it.

t (s) v (ft/s) 3 6 8 4
Solve
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The monthly cost of the water bill in a town is calculated using a piecewise function: a fixed charge of $\$10$ which includes the first $15 \text{ ft}^3…

The monthly cost of the water bill in a town is calculated using a piecewise function: a fixed charge of $\$10$ which includes the first $15 \text{ ft}^3$, a cost of $\$0,5$ per additional $\text{ft}^3$ for consumption between $15 \text{ ft}^3$ and $30 \text{ ft}^3$, and a cost of $\$1,2$ for each $\text{ft}^3$ exceeding $30 \text{ ft}^3$. Write the algebraic expression of the cost function $C(x)$ in terms of the total cubic feet consumed $x$.

Solve

Absolute value as a piecewise function

Graph of y equals the absolute value of x squared minus 9: the part of the parabola below the x-axis is flipped upward y = |x² − 9| x² − 9 (dashed) x = −3 x = 3
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Express the function $f(x) = |x^2 - 5x + 6|$ as a piecewise function without using absolute value. Indicate in which intervals the original quadratic function was…

Express the function $f(x) = |x^2 - 5x + 6|$ as a piecewise function without using absolute value. Indicate in which intervals the original quadratic function was negative before taking the absolute value.

Solve

Periodic functions: the sine curve

Graph of the buoy height: a wave with midline 4, maximum 6, minimum 2 and period 12 seconds max 6 mid 4 min 2 period = 12 sec 0 6 12 18 24 t (sec) d (ft)
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The height $h(t)$ in feet of a Ferris wheel car above the ground as a function of time $t$ in minutes is given by $h(t) = 12 + 10\sin\left(\frac{\pi}{4}t\right)$. What…

The height $h(t)$ in feet of a Ferris wheel car above the ground as a function of time $t$ in minutes is given by $h(t) = 12 + 10\sin\left(\frac{\pi}{4}t\right)$. What is the maximum and minimum height reached by the Ferris wheel? How long does it take to complete one full revolution?

Solve

From conditions to a formula

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The trajectory of a projectile describes a parabola with equation $y = ax^2 + bx + c$. Knowing that the projectile is launched from the point $(0, 3)$, reaches its…

The trajectory of a projectile describes a parabola with equation $y = ax^2 + bx + c$. Knowing that the projectile is launched from the point $(0, 3)$, reaches its maximum height at the point $(2, 7)$, and falls to the ground, find the equation of the parabola and determine at what horizontal distance from the launch point it will impact.

Solve
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The graph shows the intersection between the line $y = -x + 5$ and the hyperbola $y = \frac{4}{x}$. Find the exact coordinates of the points of intersection $A$ and $B$.

The graph shows the intersection between the line $y = -x + 5$ and the hyperbola $y = \frac{4}{x}$. Find the exact coordinates of the points of intersection $A$ and $B$.

X Y A B
Solve
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Determine the values of the parameters $a$, $b$, and $c$ of the rational function $f(x) = \frac{ax + 2}{bx + c}$, knowing that it has a vertical asymptote at $x = 1$, a…

Determine the values of the parameters $a$, $b$, and $c$ of the rational function $f(x) = \frac{ax + 2}{bx + c}$, knowing that it has a vertical asymptote at $x = 1$, a horizontal asymptote at $y = 3$, and passes through the point $(2, 8)$.

Solve

Back to the start: Mateo's scooter fare is one function, $S(m) = 0.25m + 1$. As a formula it shows the $\$1$ start and the $\$0.25$ rate, as a table it gives sample costs, and as a graph it is a line with $y$-intercept $1$ and slope $\tfrac{1}{4}$. Every other family on this page works the same way.

Summary

See all the exercises in this section