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Precalculus · Mathematics
Functions · Real functions

Transformations of Functions

Before you start, make sure you know: Basic concepts (Algebra 1)
Before you start, make sure you know: Representation of functions (Algebra 1)

At the Albuquerque Balloon Fiesta, two hot air balloons descend with exactly the same flight plan, but the second one starts 10 minutes later. Its graph is the same picture, just slid to the right. Recognizing "same picture, moved or reshaped" saves you from studying a function from scratch every time. How would you write the second balloon's altitude using the first one's formula?

Translations: sliding a graph without changing its shape

Play with the sliders: the blue curve is $y=x^2$, the other one is $y=(x-h)^2+k$.

The parabola y = f(x) in solid blue, a dashed copy shifted up by 2 units, and a dashed copy shifted 4 units to the right. f(x) f(x) + 2 f(x − 4)

Shifts carry every special point along: if $f$ has a vertex at $(p, q)$, then $f(x-h)+k$ has its vertex at $(p+h,\, q+k)$.

A delay in time is a horizontal shift. If something starts $d$ units later, replace $t$ by $t-d$. If it starts $d$ units earlier, replace $t$ by $t+d$.

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Given the function $f(x) = x^2 - 3x$, write the algebraic expression of the function $g(x)$ obtained by translating the graph of $f(x)$ four units to the left and two…

Given the function $f(x) = x^2 - 3x$, write the algebraic expression of the function $g(x)$ obtained by translating the graph of $f(x)$ four units to the left and two units upward.

Solve
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A hot air balloon descends at a constant speed. Its altitude in feet is given by $A(t) = 800 - 50t$, where $t$ is the time in minutes. A second balloon begins its…

A hot air balloon descends at a constant speed. Its altitude in feet is given by $A(t) = 800 - 50t$, where $t$ is the time in minutes. A second balloon begins its descent $10$ minutes later with exactly the same flight profile. Write the expression for the altitude of the second balloon $B(t)$ as a function of $A(t)$ and expand its final algebraic expression.

Solve
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The monthly profit of a small tech company, in thousands of dollars, is modeled by the function $B(x) = -2x^2 + 12x - 10$, where $x$ represents the month of the year…

The monthly profit of a small tech company, in thousands of dollars, is modeled by the function $B(x) = -2x^2 + 12x - 10$, where $x$ represents the month of the year ($x=1$ for January, etc.). The company decides to delay the launch of its marketing campaign by one month, which means a horizontal translation of the profit curve, and also assumes an increase in fixed costs of $3$ thousand dollars per month. Find the new expression for the profit function $N(x)$ and determine in which month the maximum profit will now be reached.

Solve

Stretches, compressions, and reflections

Play a video at double speed: everything happens in half the time. The picture of "loudness versus time" gets squeezed horizontally. That is the idea behind changing $x$ inside the function.

The curve $y=x^2-3x$ and $y=a(x^2-3x)$. Try negative values of $a$.

Translating words into transformations

In words Formula
The output is $c$ times as big $c\,f(x)$
$r\%$ more output $\left(1+\tfrac{r}{100}\right)f(x)$, for example $1.2f(x)$ for 20% more
A fixed amount $d$ is added to the output $f(x)+d$
The same output is reached at an input $c$ times larger $f\!\left(\tfrac{x}{c}\right)$
The same output is reached at an input $c$ times smaller (for example, $c$ times faster) $f(cx)$

When you are unsure, test one value. If the old function gave a result at input 6 and the new one must give it at input 18, then $N(18)=C(6)$, which means $N(x)=C(x/3)$.

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The function $C(x)$ represents the cost in dollars of producing $x$ electronic components. Due to a technological improvement in the assembly line, it is now possible to…

The function $C(x)$ represents the cost in dollars of producing $x$ electronic components. Due to a technological improvement in the assembly line, it is now possible to produce triple the number of components for exactly the same total cost. Express the new cost function $N(x)$ in terms of the original function $C(x)$.

Solve
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Given the elementary function $f(x) = \frac{1}{x}$, state which geometric transformations (translations, stretches, reflections) must be applied successively, and in…

Given the elementary function $f(x) = \frac{1}{x}$, state which geometric transformations (translations, stretches, reflections) must be applied successively, and in what order, to obtain the function $g(x) = -\frac{3}{x} + 2$.

Solve

Combining transformations: order matters

Flow diagram: x goes to b(x − h) inside the parentheses, then f is applied, then the outside operations multiply by a and add k. x first, inside b(x − h) apply f f(b(x − h)) then: ·a + k a·f(b(x − h)) + k inside the parentheses first, outside after

There is usually more than one road. Shift $\sqrt{x}$ left 6 units first: $\sqrt{x+6}$. Then compress by $\tfrac13$, replacing $x$ by $3x$: $\sqrt{3x+6}$. It is the same function as "compress, then shift left 2." The shift just has to be recomputed.

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Given the elementary function $f(x) = \sqrt{x}$, we want to obtain the function $g(x) = \sqrt{4x - 12} + 5$. Explain in detail two different sequences of geometric…

Given the elementary function $f(x) = \sqrt{x}$, we want to obtain the function $g(x) = \sqrt{4x - 12} + 5$.

Explain in detail two different sequences of geometric transformations (altering the order of the horizontal translations and stretches) that allow $g(x)$ to be obtained from $f(x)$. Prove algebraically that both sequences lead to the same expression.

Solve
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A parabola has its vertex at the origin and passes through the point $(2, 4)$. The following transformations are applied to it sequentially: 1. A horizontal compression…

A parabola has its vertex at the origin and passes through the point $(2, 4)$. The following transformations are applied to it sequentially:

  1. A horizontal compression that multiplies the x-coordinates of its points by $\frac{1}{3}$.

  2. A translation of $5$ units to the left.

  3. A reflection in the x-axis.

  4. A translation of $7$ units upwards.

Find the analytical expression of the final function $g(x)$ and determine the exact coordinates of its new vertex and its points of intersection with the axes.

Solve

Tracking points

You do not always know a formula for $f$, only a few key points of its graph. The transformations tell you exactly where each point goes.

A blue tent-shaped graph f with vertices at (−2, 0), (0, 2), (2, 0) and an orange tent g with vertices at (1, 1), (3, 2), (5, 1). f g (0, 2) (3, 2)
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The graph of a function $f(x)$ passes through the point $P(-3, 5)$. Determine the coordinates of the corresponding point on the graphs of the following transformed…

The graph of a function $f(x)$ passes through the point $P(-3, 5)$. Determine the coordinates of the corresponding point on the graphs of the following transformed functions:

  • $g(x) = -f(x)$

  • $h(x) = f(-x)$

  • $i(x) = 2f(x)$

  • $j(x) = f(x) - 4$

Solve
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The efficiency of a solar panel throughout the day is given by a function $E(t)$. A new model of panel is installed that starts generating energy $2$ hours earlier and,…

The efficiency of a solar panel throughout the day is given by a function $E(t)$. A new model of panel is installed that starts generating energy $2$ hours earlier and, due to a special graphene coating, generates $15\%$ more energy at each equivalent instant. Express the new efficiency function $N(t)$ in terms of $E(t)$. If the original panel reached its maximum efficiency at 2:00 p.m., at what time will the new panel reach it?

Solve
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The graph of the function $f(x)$ is formed by two line segments joining the points $(-4, -2)$, $(0, 4)$, and $(4, -2)$. A new function is defined by the transformation…

The graph of the function $f(x)$ is formed by two line segments joining the points $(-4, -2)$, $(0, 4)$, and $(4, -2)$. A new function is defined by the transformation $g(x) = -f\left(\frac{x}{2}\right) + 3$.

  • Describe the ordered sequence of geometric transformations applied to $f(x)$.

  • Calculate the exact coordinates of the new vertices of the graph of $g(x)$.

X Y (−4, −2) (0, 4) (4, −2) f(x)
Solve

Domain and range after a transformation

Think of the domain and range of $f$ as a box on the coordinate plane. A transformation moves and reshapes the box.

The domain-range box of f, from x = −2 to 5 and y = 0 to 4, and the larger box of g(x) = 2f(x+1) − 3, from x = −3 to 4 and y = −3 to 5. box of f box of g
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Observe the graph of the function $f(x)$ defined in the interval $[-4, 4]$. Determine the domain and the range of the transformed function $g(x) = f(x-3) + 1$.

Observe the graph of the function $f(x)$ defined in the interval $[-4, 4]$. Determine the domain and the range of the transformed function $g(x) = f(x-3) + 1$.

X Y −4 (−2, 3) (1, −2) 4 f(x)
Solve
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Given an arbitrary function $f(x)$ whose domain is the interval $[-6, 8]$ and whose range is the interval $[-4, 12]$, a new function is defined by the expression…

Given an arbitrary function $f(x)$ whose domain is the interval $[-6, 8]$ and whose range is the interval $[-4, 12]$, a new function is defined by the expression $h(x) = -2f\left(3 - \frac{x}{2}\right) + 5$.

Calculate, showing your reasoning and detailing the effects of each applied transformation, the domain and the range of the function $h(x)$.

Solve

Modeling: waves, growth, and finding parameters

Sinusoidal waves

Sines and cosines are transformed like any other function.

Shifting an exponential

Shifting an exponential graph is the same as stretching it vertically. For $P(t)=a\cdot b^{t}$:

$$P(t+c)=a\,b^{t+c}=\big(a\,b^{c}\big)\,b^{t}.$$

For example, if $P(t)=50\cdot 2^{t}$ and $Q(t)=P(t+3)$, then $Q(t)=50\cdot 2^{3}\cdot 2^{t}=400\cdot 2^{t}$. The shifted copy is also a stretched copy.

Finding parameters from conditions

When a problem asks for $g(x)=a\,f(bx-c)+d$ with given conditions:

  1. Turn each sentence into one effect: "twice as wide" means $b=\tfrac12$ (horizontal stretch), "inverted" means $a<0$, "moved 4 right" is a shift $h=4$, "lowest point at height 10" uses the range of $f$.

  2. Rewrite the inside as $bx-c=b\!\left(x-\tfrac{c}{b}\right)$. The shift is $h=\tfrac{c}{b}$, so $c=bh$.

  3. Use the range of $f$ and the rule "range of $g$ is $a\cdot(\text{range of } f)+d$" for conditions about highest or lowest values.

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In an acoustics study, a base sound wave is modeled by the function $S(t) = \sin(t)$. For an experiment, the original wave is amplified by multiplying its amplitude by…

In an acoustics study, a base sound wave is modeled by the function $S(t) = \sin(t)$. For an experiment, the original wave is amplified by multiplying its amplitude by $4$ and is made higher-pitched by doubling its frequency. In addition, a delay of $\frac{\pi}{4}$ seconds is introduced in the emission. Write the analytical expression of the new sound wave $W(t)$ and calculate its new period.

Solve
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A culture of bacteria grows according to the function $N(t) = 200 \cdot 3^{t/2}$, where $t$ is the time in hours. A second culture $M(t)$ starts with a quarter of the…

A culture of bacteria grows according to the function $N(t) = 200 \cdot 3^{t/2}$, where $t$ is the time in hours. A second culture $M(t)$ starts with a quarter of the initial population of the first, but its growth rate is identical and it started being measured $4$ hours earlier. Express $M(t)$ in terms of $N(t)$ and simplify the resulting expression to check if both populations will be equal at any point.

Solve
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An engineer designs the profile of a suspension bridge using the curve $f(x) = e^{-x^2}$ as a model. Due to the geological requirements of the terrain, they need to…

An engineer designs the profile of a suspension bridge using the curve $f(x) = e^{-x^2}$ as a model. Due to the geological requirements of the terrain, they need to propose a new profile $g(x) = a \cdot f(b \cdot x - c) + d$ that simultaneously meets the following conditions:

  • It must be twice as wide as the original design.

  • The center of symmetry of the bridge must be translated $4$ units to the right.

  • The profile must be inverted (opening upwards instead of downwards), without changing its vertical scale.

  • The minimum height of the new profile must be situated exactly $10$ feet above ground level.

Determine analytically the precise values of the parameters $a$, $b$, $c$ and $d$.

Solve

Absolute value of a function: $|f(x)|$

Some problems call absolute value the modulus. It is the same thing.

The parabola f(x) = x² − 4, dashed where it dips below the x-axis, and the graph of |f(x)| in solid blue, with the dipping part reflected upward. dashed: f(x) solid: |f(x)|

To graph $|f|$:

  1. Find where $f(x)=0$. These are the x-intercepts, and the graph stays there.

  2. Reflect only the pieces below the axis. A vertex at $(p, q)$ with $q<0$ goes to $(p, -q)$.

  3. The x-intercepts usually become sharp corners.

Absolute value of a wave

For $y=|A\sin(Bx)|$ the negative arches flip up and become copies of the positive ones, so the period is cut in half: from $\tfrac{2\pi}{|B|}$ to $\tfrac{\pi}{|B|}$. The maximum $|A|$ is reached wherever $\sin(Bx)=\pm 1$.

For example, $y=|3\cos 2x|$: the period of $3\cos 2x$ is $\pi$, so the new period is $\tfrac{\pi}{2}$. The maximum 3 is reached where $\cos 2x=\pm1$, at $x=0,\ \tfrac{\pi}{2},\ \pi,\dots$

If the wave is not centered on the x-axis, subtract its midline first. For example, $|L(t)-D|$ takes the wave $L(t)=A\sin(\cdot)+D$ back to $A\sin(\cdot)$ before folding it.

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From the graph of the function $f(x)$ shown in the figure, describe the geometric steps necessary to obtain the graph of the function $g(x) = |f(x)|$ and calculate the…

From the graph of the function $f(x)$ shown in the figure, describe the geometric steps necessary to obtain the graph of the function $g(x) = |f(x)|$ and calculate the coordinates of the new vertices or inflection points.

X Y 2 −4 f(x)
Solve
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Express the function $g(x) = |-x^2 + 4|$ as a piecewise-defined function, removing the absolute value bars and clearly indicating the intervals where the original…

Express the function $g(x) = |-x^2 + 4|$ as a piecewise-defined function, removing the absolute value bars and clearly indicating the intervals where the original expression changes sign.

Solve
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The figure shows the light curve of a variable star, modeled by the function $L(t) = 4 \sin\left(\frac{\pi}{6}t\right) + 10$, where $t$ is measured in days and $L$ in…

The figure shows the light curve of a variable star, modeled by the function $L(t) = 4 \sin\left(\frac{\pi}{6}t\right) + 10$, where $t$ is measured in days and $L$ in units of luminosity. A dense cloud of cosmic dust obscures the star in such a way that the observed luminosity $O(t)$ from Earth is exactly the modulus of the difference between $L(t)$ and its mean luminosity.

Determine the analytical expression of $O(t)$, calculate its new period and find at what instants $t \in [0, 12]$ the observed luminosity is maximum.

t (days) L(t) 10 14 3 6 9 12 L(t)
Solve

Absolute value inside: $f(|x|)$

Putting the absolute value on the input does something different.

Left: the graph of y = |x| − 3, a V with its vertex at (0, −3). Right: the graph of y = |x − 3|, a V with its vertex at (3, 0). (0, −3) y = |x| − 3 (3, 0) y = |x − 3|

The two look similar but are very different. $|x|-3$ is "take the V, then shift down 3." $|x-3|$ is "shift the line, then fold at the x-intercept."

For nested absolute values, work from the inside out, one layer at a time.

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Match each of the analytical expressions with the corresponding panel in the figure, knowing that they all derive from modulus transformations applied to the base…

Match each of the analytical expressions with the corresponding panel in the figure, knowing that they all derive from modulus transformations applied to the base function $y = x - 3$.

  1. $y = |x| - 3$

  2. $y = ||x-3| - 2|$

  3. $y = ||x| - 3|$

  4. $y = |x-3| - 2$

A B C D
Solve

Rational functions as shifted hyperbolas

A rational function like $\dfrac{2x+7}{x+1}$ looks complicated, but a little division reveals a transformed copy of $y=\tfrac1x$.

To get this form from $\dfrac{px+q}{x-h}$, divide the polynomials (long division, or rewrite the numerator using the denominator).

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Express the rational function $f(x) = \frac{2x + 7}{x + 1}$ in the form $f(x) = k + \frac{m}{x+1}$, by carrying out polynomial division. From this result, describe step…

Express the rational function $f(x) = \frac{2x + 7}{x + 1}$ in the form $f(x) = k + \frac{m}{x+1}$, by carrying out polynomial division. From this result, describe step by step the geometric transformations that must be applied to the rectangular hyperbola $y = \frac{1}{x}$ to obtain the graph of $f(x)$.

Solve

Symmetry and period of transformed functions

Recall that $f$ is even if $f(-x)=f(x)$ and odd if $f(-x)=-f(x)$. Shifts move the center of symmetry.

For example, $f(x)=(x-1)^3+2$ gives $f(x+1)-2=x^3$, which is odd. So the graph is symmetric about the point $(1,2)$. For the same reason, the hyperbola $k+\tfrac{m}{x-h}$ is symmetric about its center $(h,k)$.

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Find the values of the parameters $a$ and $b$ so that the graph of the rational function $f(x) = \frac{ax + 3}{x + b}$ is symmetrical about the point $C(4, 2)$. Hint:…

Find the values of the parameters $a$ and $b$ so that the graph of the rational function $f(x) = \frac{ax + 3}{x + b}$ is symmetrical about the point $C(4, 2)$.

Hint: Remember that a function $f(x)$ is symmetrical about a point $(h, k)$ if the function translated to the origin, $g(x) = f(x+h) - k$, turns out to be an odd function.

Solve
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Let $f(x)$ be an odd, periodic real function with period $T=6$. From it, the transformed function $g(x) = f(x-2) + f(x+2)$ is defined. Prove analytically whether the…

Let $f(x)$ be an odd, periodic real function with period $T=6$. From it, the transformed function $g(x) = f(x-2) + f(x+2)$ is defined.

Prove analytically whether the function $g(x)$ is even, odd or neither. Also determine whether $g(x)$ is periodic and, if so, calculate its minimum period.

Solve

Changing the axes, and the ellipse

Moving the coordinate system

Sometimes the graph stays put and the axes change. Moving the origin to the right is the same as moving the picture to the left. This is why the formulas look "backward."

Careful: a halved unit means $v=\tfrac12$, so all the $y$-numbers get doubled.

Building an ellipse from a circle

The upper half of the unit circle is $y=\sqrt{1-x^2}$. Stretch it and shift it to get a half-ellipse.

The small unit semicircle at the origin and a large half-ellipse centered at (2, 1) with horizontal semi-axis 5 and vertical semi-axis 3. center (2, 1); a = 5, b = 3 y = √(1 − x²)

A semicircle of radius $R$ is the special case $a=b=R$ with no shifts: $R\sqrt{1-(x/R)^2}=\sqrt{R^2-x^2}$.

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Let the function be $f(x) = \ln(x)$. A change of reference system is made in the Cartesian plane so that the new origin is located at the point $(-3, 2)$ of the old…

Let the function be $f(x) = \ln(x)$. A change of reference system is made in the Cartesian plane so that the new origin is located at the point $(-3, 2)$ of the old system, the positive direction of the x-axis is reversed, and the unit of measurement of the y-axis is halved. Write the equation of the curve in the new coordinate system.

Solve
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A programmed trajectory for a robotic arm is given by the function $y = \sqrt{R^2 - x^2}$, which describes a semicircle of radius $R$ centered at the origin. The design…

A programmed trajectory for a robotic arm is given by the function $y = \sqrt{R^2 - x^2}$, which describes a semicircle of radius $R$ centered at the origin. The design team wishes to program a new elliptical trajectory $E(x)$ that has its center at the point $(h, k)$, a horizontal semi-axis of length $a$ and a vertical semi-axis of length $b$ (representing only the upper half of the ellipse).

Express the final function $E(x)$, clearly indicating the composition of geometric transformations applied to the base function $y = \sqrt{1 - x^2}$ (semicircle of radius $1$).

Solve

Back to the start: if $h(t)$ is the altitude of the first balloon after $t$ minutes, the second balloon, which leaves 10 minutes later, is described exactly by $g(t)=h(t-10)$: a horizontal shift of 10 units to the right.

Summary

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