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Functions · Real functions

Characteristics of Functions

Before you start, make sure you know: Basic concepts (High School Year 1 (semesters 1 and 2))
Before you start, make sure you know: Inequalities in one variable (High School Year 1 (semesters 1 and 2))

A CFE app shows you how much you spend on electricity depending on the days of the month. Which values of $x$ make sense? When does the cost go up or down? What is the maximum? To answer these questions we always ask the function the same things: where it is defined, where it crosses the axes, where it is positive or negative, what values it takes, and whether it has symmetry. At the end of the page we come back to the question of how to answer all of this in an orderly way.

Domain with several restrictions

Strip diagram representing the intersection between the region where the radicand is nonnegative and the region where the denominator is nonzero. radicand ≥ 0 denominator ≠ 0 final domain: the intersection
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Determine the domain of the rational function $f(x) = \frac{x-1}{x^2-9}$.

Determine the domain of the rational function $f(x) = \frac{x-1}{x^2-9}$.

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

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

Solve
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Find the domain of the logarithmic function $s(x) = \log_3(x+2)$.

Find the domain of the logarithmic function $s(x) = \log_3(x+2)$.

Solve
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Find the domain of the function $f(x) = \sqrt{\frac{x+1}{x-3}}$.

Find the domain of the function $f(x) = \sqrt{\frac{x+1}{x-3}}$.

Solve
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Determine the domain of the function $f(x) = \ln(x^2 - 4x + 3)$.

Determine the domain of the function $f(x) = \ln(x^2 - 4x + 3)$.

Solve
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Find the domain of the function $f(x) = \sqrt{\log_2(x-3)}$, justifying your answer.

Find the domain of the function $f(x) = \sqrt{\log_2(x-3)}$, justifying your answer.

Solve

Intercepts and sign

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Find the axis intercepts of the polynomial function $h(x) = x^2 - 5x + 6$.

Find the axis intercepts of the polynomial function $h(x) = x^2 - 5x + 6$.

Solve
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Determine the intervals in which the function $q(x) = -3x + 12$ is positive and those in which it is negative.

Determine the intervals in which the function $q(x) = -3x + 12$ is positive and those in which it is negative.

Solve
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Find the axis intercepts and study the sign of the rational function $g(x) = \frac{x^2-4}{x-1}$.

Find the axis intercepts and study the sign of the rational function $g(x) = \frac{x^2-4}{x-1}$.

Solve
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Given the piecewise function: $f(x) = \begin{cases} 2x+6 & \text{if } x < -1 \\ x^2+3 & \text{if } x \ge -1 \end{cases}$ Find its axis intercepts and study its sign…

Given the piecewise function:

$f(x) = \begin{cases} 2x+6 & \text{if } x < -1 \\ x^2+3 & \text{if } x \ge -1 \end{cases}$

Find its axis intercepts and study its sign across its whole domain.

Solve

Range (image) of a function

Graph of an upward-opening parabola with vertex at (0, 4); the line y = 4 passes through the vertex and marks the minimum of the range, the ray [4, +∞) on the vertical axis. 4 y = 4 (minimum of the range)

To find it: for a parabola, use the vertex; in general, solve for $x$ in terms of $y$ (that is, look for the inverse function), and the domain of the inverse is the range of $f$.

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State the range of the quadratic function $r(x) = x^2 + 4$.

State the range of the quadratic function $r(x) = x^2 + 4$.

Solve
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Find the inverse function of $f(x) = \frac{2x-5}{x+1}$ and use it to determine the range of the function $f(x)$.

Find the inverse function of $f(x) = \frac{2x-5}{x+1}$ and use it to determine the range of the function $f(x)$.

Solve

Symmetry: even and odd functions

Graph symmetric about the vertical axis showing the equality of heights f(-x) = f(x) for two symmetric values on the horizontal axis. x−x
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Study the symmetry (even, odd or neither) of the polynomial function $p(x) = x^4 - 2x^2 + 7$.

Study the symmetry (even, odd or neither) of the polynomial function $p(x) = x^4 - 2x^2 + 7$.

Solve
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Determine analytically whether the function $h(x) = \frac{x^3}{x^2+1}$ is even, odd or has no symmetry.

Determine analytically whether the function $h(x) = \frac{x^3}{x^2+1}$ is even, odd or has no symmetry.

Solve
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Prove analytically that the function $f(x) = \ln\left(\frac{1-x}{1+x}\right)$ is odd and determine its domain.

Prove analytically that the function $f(x) = \ln\left(\frac{1-x}{1+x}\right)$ is odd and determine its domain.

Solve

Increasing and decreasing behavior, extrema, and quadratic functions

For a parabola $f(x)=ax^2+bx+c$ the only extremum is the vertex, at $x_v=-\dfrac{b}{2a}$. If $a<0$ it is a maximum; if $a>0$, a minimum.

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From the graphical representation of the parabola $y = f(x)$, state its intervals of increase and decrease, as well as the coordinates of its relative extremum.

From the graphical representation of the parabola $y = f(x)$, state its intervals of increase and decrease, as well as the coordinates of its relative extremum.

X Y V(2, 4) 0 4
Solve
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A projectile is launched vertically upward. The height $h(t)$ in meters that it reaches after $t$ seconds is given by the function $h(t) = -5t^2 + 20t + 1$. Determine at…

A projectile is launched vertically upward. The height $h(t)$ in meters that it reaches after $t$ seconds is given by the function $h(t) = -5t^2 + 20t + 1$. Determine at what time it reaches its maximum height and what this maximum height is.

Solve
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A farmer has $100$ meters of fencing to enclose a rectangular vegetable garden taking advantage of an existing stone wall (no fencing is needed on that side). If $x$ is…

A farmer has $100$ meters of fencing to enclose a rectangular vegetable garden taking advantage of an existing stone wall (no fencing is needed on that side). If $x$ is the length of the sides perpendicular to the wall, the function describing the area is $A(x) = x(100-2x)$. Determine the domain of the function in the context of the problem and calculate the dimensions that maximize the area.

Solve
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Determine the coefficients $a$, $b$ and $c$ of the quadratic function $f(x) = ax^2 + bx + c$ knowing that its vertex is the point $V(3, -4)$ and that it intersects the…

Determine the coefficients $a$, $b$ and $c$ of the quadratic function $f(x) = ax^2 + bx + c$ knowing that its vertex is the point $V(3, -4)$ and that it intersects the x-axis at $x = 1$.

Solve
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The average monthly cost (in pesos) per unit produced in an electronic components factory is given by the function $C_m(x) = \frac{6\,000x + 24\,000}{x}$, where $x$ is…

The average monthly cost (in pesos) per unit produced in an electronic components factory is given by the function $C_m(x) = \frac{6\,000x + 24\,000}{x}$, where $x$ is the number of units produced ($x > 0$). Determine the domain in the context of the problem, study its sign and prove analytically in which intervals the average cost is increasing or decreasing.

Solve

Asymptotes

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Find the values of the parameters $a$ and $b$ so that the function $f(x) = \frac{x^2+a}{x-b}$ has domain $\mathbb{R} \setminus \{2\}$ and intersects the x-axis at the…

Find the values of the parameters $a$ and $b$ so that the function $f(x) = \frac{x^2+a}{x-b}$ has domain $\mathbb{R} \setminus \{2\}$ and intersects the x-axis at the points $x = 4$ and $x = -4$.

Solve

Periodic functions and complete analysis

To analyze a complete graph, answer in order: domain, range, intercepts with the axes, sign, symmetry, asymptotes, increasing and decreasing behavior, and extrema. That settles the opening question: you don't guess, you go through the checklist.

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Observe the graph of the following periodic function modelling the voltage in an electronic circuit. Determine its period $T$ and calculate the value of $f(17)$.

Observe the graph of the following periodic function modelling the voltage in an electronic circuit. Determine its period $T$ and calculate the value of $f(17)$.

t f(t) 4 8 12 2 −2
Solve
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The attached graph shows the height $h(t)$ in meters of a Ferris wheel capsule as a function of time $t$ in minutes. Given that the motion is modeled by a trigonometric…

The attached graph shows the height $h(t)$ in meters of a Ferris wheel capsule as a function of time $t$ in minutes. Given that the motion is modeled by a trigonometric function, determine its period, the maximum and minimum heights reached by the capsule, and the times at which they are reached during the first full cycle.

15 m 10 m
Solve
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From the graph of the function $y = f(x)$, perform a complete analysis stating: domain, range, symmetry, equations of the asymptotes, relative extrema and intervals of…

From the graph of the function $y = f(x)$, perform a complete analysis stating: domain, range, symmetry, equations of the asymptotes, relative extrema and intervals of positive and negative sign.

X Y 1 2 −1 −2 1 2
Solve

Summary

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