Back to homeMathematics · 4th ESO A · Change subject
Start for free
ESO Y4A · Mathematics
functions · Functions

Symmetry of a function

The cable of a suspension bridge has the same shape to the left and to the right of the centre: if you know half of it, you know the whole bridge. That is symmetry, and in maths it can be checked without drawing anything, just by calculating $f(-x)$.

Before you start, make sure you know: Characteristics of a function (3rd ESO)
Before you start, make sure you know: Operations with powers (3rd ESO)

Even functions: symmetry about the Y-axis

Graph symmetric about the Y-axis where the symmetric points a and minus a have the same height f(−a)f(a) axis of symmetry
Practice★☆☆Not started
Determine algebraically whether the function $f(x) = 3x^4 - 2x^2 + 5$ is even, odd or has no symmetry.

Determine algebraically whether the function $f(x) = 3x^4 - 2x^2 + 5$ is even, odd or has no symmetry.

Solve
Practice★☆☆Not started
Observe the following graph of a function $f(x)$. From its representation, determine what type of symmetry it possesses and calculate the value of $f(-2)$ knowing that…

Observe the following graph of a function $f(x)$. From its representation, determine what type of symmetry it possesses and calculate the value of $f(-2)$ knowing that $f(2) = -2$.

X Y 2 −2 −2 f(2) f(−2) = ? f(x)
Solve

Odd functions: symmetry about the origin

Animation of a function with odd symmetry: the right-hand half of the graph, its point (a, f(a)) and its label rotate through a half-turn about the origin and land on the left-hand half, at the point (−a, −f(a)); then they return to their place. (a, f(a)) (−a, −f(a))
Practice★☆☆Not started
Check analytically whether the rational function $g(x) = \frac{2x}{x^2 + 1}$ shows any type of symmetry.

Check analytically whether the rational function $g(x) = \frac{2x}{x^2 + 1}$ shows any type of symmetry.

Solve
Practice★☆☆Not started
Study the symmetry of the polynomial function $h(x) = x^3 - 4x + 1$.

Study the symmetry of the polynomial function $h(x) = x^3 - 4x + 1$.

Solve
Practice★☆☆Not started
Classify the following elementary functions as even, odd or having no symmetry: $y = x$, $y = x^2$, $y = \frac{1}{x}$, $y = |x|$.

Classify the following elementary functions as even, odd or having no symmetry: $y = x$, $y = x^2$, $y = \frac{1}{x}$, $y = |x|$.

Solve

Using symmetry to deduce values

Practice★☆☆Not started
The graph below represents the function $g(x)$. Visually identify its symmetry and find $g(-3)$ if we know that $g(3) = 2$. You can do it on paper and send a photo with…

The graph below represents the function $g(x)$. Visually identify its symmetry and find $g(-3)$ if we know that $g(3) = 2$.

X Y 3 −3 g(3)=2 g(−3)=? g(x)

You can do it on paper and send a photo with your answer.

Solve
Practice★☆☆Not started
A function $f(x)$ passes through the point $(2, 5)$. If we know that it is an even function, through which other point must it pass? What if it were an odd function?

A function $f(x)$ passes through the point $(2, 5)$. If we know that it is an even function, through which other point must it pass? What if it were an odd function?

Solve
Practice★★☆Not started
The main cable of a suspension bridge takes the form of a parabola described by the function $f(x) = 0,05x^2 + 10$, where $x$ is the horizontal distance in metres from…

The main cable of a suspension bridge takes the form of a parabola described by the function $f(x) = 0,05x^2 + 10$, where $x$ is the horizontal distance in metres from the centre of the bridge. Test its symmetry algebraically and explain the physical meaning of this result for the structure of the bridge.

Solve
Practice★★☆Not started
The profile of a wind turbine blade is modelled using an odd function of the form $f(x) = ax^3$. If the tip of the blade is located at the coordinates $(15, 30)$ in cm,…

The profile of a wind turbine blade is modelled using an odd function of the form $f(x) = ax^3$. If the tip of the blade is located at the coordinates $(15, 30)$ in cm, at what coordinates will the opposite tip be located? Calculate also the value of the parameter $a$.

Solve

Symmetry in rational and combined functions

When $f(x)$ is a fraction, $f(-x)$ is calculated by substituting in the numerator and the denominator separately; it is best to simplify the signs carefully.

Practice★☆☆Not started
Reason whether the product of an even function and an odd function results in an even function, an odd function, or a function with no symmetry. You can use simple…

Reason whether the product of an even function and an odd function results in an even function, an odd function, or a function with no symmetry. You can use simple examples such as $x^2$ and $x$ to illustrate your conclusion.

Solve
Practice★★☆Not started
Study the symmetry of the function $f(x) = \frac{x^3}{\sqrt{x^2+4}}$ algebraically.

Study the symmetry of the function $f(x) = \frac{x^3}{\sqrt{x^2+4}}$ algebraically.

Solve
Practice★★☆Not started
Find the value that the parameter $k$ must take for the function $f(x) = 2x^2 + kx + 5$ to be an even function across its entire domain.

Find the value that the parameter $k$ must take for the function $f(x) = 2x^2 + kx + 5$ to be an even function across its entire domain.

Solve
Practice★★☆Not started
Given two functions, $f(x)$ (even) and $g(x)$ (odd), analyse the symmetry of the sum function $h(x) = f(x) + g(x)$. Verify this using the functions $f(x) = x^2$ and…

Given two functions, $f(x)$ (even) and $g(x)$ (odd), analyse the symmetry of the sum function $h(x) = f(x) + g(x)$. Verify this using the functions $f(x) = x^2$ and $g(x) = x$.

Solve

Back to the beginning: The suspension bridge cable represents an even function: if we place the origin at its lowest point, the height at any distance $x$ to the right is the same as the height at the same distance to the left because $f(-x) = f(x)$.

Summary

See all the exercises in this section