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ESO Y4B · Mathematics
Functions · Functions

Basic concepts

An electricity bill depends on the kWh consumed; the distance travelled by an object in free fall depends on the time elapsed. In both cases there are two quantities related by a rule. This year you will deal with that relationship with the rigour you will need at Bachillerato: formal notation, the exact domain, and a first measure of how a function changes, the average rate of change, which is the direct forerunner of the derivative.

Before you start, make sure you know: The concept of a function (3rd ESO)
Before you start, make sure you know: Quadratic equations (3rd ESO)

Function, domain and variable

In $C(x) = 0{,}15x + 8$, $x$ is the number of kWh consumed and $C(x)$ the cost in euros: $x$ is chosen, $C(x)$ is calculated.

Diagram of a function as a process that assigns to each input value x a single output value f(x) fy = f(x) x f(x) each x has a single f(x)
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Given the polynomial function $f(x) = 2x^2 - 5x + 1$, calculate the images for the values $x = -2$, $x = 0$ and $x = 3$.

Given the polynomial function $f(x) = 2x^2 - 5x + 1$, calculate the images for the values $x = -2$, $x = 0$ and $x = 3$.

Solve
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A bicycle hire service charges a fixed fee of $3$ euros to register for the service, plus $1,50$ euros per hour of use. Write the algebraic expression of the function…

A bicycle hire service charges a fixed fee of $3$ euros to register for the service, plus $1,50$ euros per hour of use. Write the algebraic expression of the function that relates the total cost to the time of use, and identify which is the independent variable and which is the dependent variable.

Solve

Domain of definition

  • Polynomial (sums, differences and products of $x$): defined for every $x$, $D = \mathbb{R}$.

  • Rational (fraction with $x$ in the denominator): the values that make the denominator zero are excluded.

  • Radical with an even index ($\sqrt{}$, $\sqrt[4]{}$...): the radicand must be greater than or equal to zero.

Representation on the real number line of the simultaneous restrictions of the radical and the denominator to obtain the common region of the domain x = −4(included) x = 2(forbidden) −4−20246 Dom = [−4, 2) ∪ (2, +∞)
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Determine the domain of definition of the following functions: a) $f(x) = \frac{3}{x - 5}$ b) $g(x) = \sqrt{x + 2}$

Determine the domain of definition of the following functions:

  1. a) $f(x) = \frac{3}{x - 5}$
  2. b) $g(x) = \sqrt{x + 2}$
Solve
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Find the domain of definition of the function $f(x) = \frac{\sqrt{x + 4}}{x - 2}$.

Find the domain of definition of the function $f(x) = \frac{\sqrt{x + 4}}{x - 2}$.

Solve
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Determine analytically the domain of definition of the function $f(x) = \sqrt{\frac{x - 3}{x + 2}}$. Express the result as a union of intervals.

Determine analytically the domain of definition of the function $f(x) = \sqrt{\frac{x - 3}{x + 2}}$. Express the result as a union of intervals.

Solve

Intercepts and symmetry

Graphical comparison of an even function with symmetry about the vertical axis and an odd function with symmetry about the origin even: f(−x) = f(x) odd: f(−x) = −f(x)
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Calculate analytically the points of intersection with the x-axis and the y-axis of the function $f(x) = x^2 - 6x + 8$.

Calculate analytically the points of intersection with the x-axis and the y-axis of the function $f(x) = x^2 - 6x + 8$.

Solve
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Determine algebraically whether the following functions are even, odd, or have no symmetry: a) $f(x) = x^4 - 2x^2$ b) $g(x) = x^3 - 3x + 1$

Determine algebraically whether the following functions are even, odd, or have no symmetry:

  1. a) $f(x) = x^4 - 2x^2$
  2. b) $g(x) = x^3 - 3x + 1$
Solve

Average rate of change: how to measure a change

Its sign indicates the overall behaviour of $f$ over that particular interval: positive if $f$ increases overall from $a$ to $b$, negative if it decreases, zero if it returns to the same value.

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Calculate the average rate of change of the function $f(x) = x^2 - 4$ over the intervals $[-1, 2]$ and $[2, 5]$.

Calculate the average rate of change of the function $f(x) = x^2 - 4$ over the intervals $[-1, 2]$ and $[2, 5]$.

Solve
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The distance $d$ (in metres) covered by a free-falling object as a function of time $t$ (in seconds) is approximated by the function $d(t) = 5t^2$. Calculate the average…

The distance $d$ (in metres) covered by a free-falling object as a function of time $t$ (in seconds) is approximated by the function $d(t) = 5t^2$. Calculate the average speed of the object (which corresponds to the average rate of change) between the first and third seconds ($t \in [1, 3]$), and between the third and fifth seconds ($t \in [3, 5]$).

Solve
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Calculate the average rate of change of the function $f(x) = \frac{1}{x}$ over the intervals $[1, 2]$ and $[2, 4]$. What does the sign of the results indicate about the…

Calculate the average rate of change of the function $f(x) = \frac{1}{x}$ over the intervals $[1, 2]$ and $[2, 4]$. What does the sign of the results indicate about the monotonicity of the function over those intervals?

Solve

Asymptotes: forbidden values and long-range behaviour

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Determine analytically the equations of the vertical and horizontal asymptotes of the rational function $f(x) = \frac{2x + 1}{x - 3}$.

Determine analytically the equations of the vertical and horizontal asymptotes of the rational function $f(x) = \frac{2x + 1}{x - 3}$.

Solve
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Given the rational function $f(x) = \frac{ax^2 + 3}{2x^2 - x}$, determine the value of the parameter $a$ so that the function has a horizontal asymptote at the line…

Given the rational function $f(x) = \frac{ax^2 + 3}{2x^2 - x}$, determine the value of the parameter $a$ so that the function has a horizontal asymptote at the line $y = 4$. With this value of $a$ calculated, also find the equations of the vertical asymptotes of the function.

Solve

Piecewise functions: continuity

Piecewise-defined function with a jump discontinuity at the joining point: the first piece ends at a filled point and the second starts at an open point jump: discontinuous at the joining point
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Given the following graph of a piecewise-defined function, find the values of $f(-2)$, $f(1)$ and $f(4)$. Then, state at which points the function is discontinuous and…

Given the following graph of a piecewise-defined function, find the values of $f(-2)$, $f(1)$ and $f(4)$. Then, state at which points the function is discontinuous and the type of each discontinuity.

X Y −1 2 1 2 4
Solve
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The accompanying graph represents the height in metres of a Ferris wheel capsule as a function of time in minutes. Observe the graph and answer: a) Is it a periodic…

The accompanying graph represents the height in metres of a Ferris wheel capsule as a function of time in minutes. Observe the graph and answer:

  1. a) Is it a periodic function? If so, state its period.
  2. b) What are the maximum and minimum heights reached by the capsule?
  3. c) At what height is the capsule exactly $10$ minutes after starting to rotate?
t (min) h (m) 10 20 2 4 6 8
Solve
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Find the values of the parameters $a$ and $b$ so that the following piecewise-defined function is continuous throughout its domain:…

Find the values of the parameters $a$ and $b$ so that the following piecewise-defined function is continuous throughout its domain:

$f(x) = \begin{cases} 2x + a & \text{if } x < 1 \\ x^2 - 3x + 5 & \text{if } 1 \le x < 4 \\ bx - 1 & \text{if } x \ge 4 \end{cases}$

Solve

Summary

See all the exercises in this section