Define each of the following:
(i) injective function
(ii) surjective function
(iii) bijective function
(iv) many - one function
(v) into function
Give an example of each type of functions.
1)injective function
Definition: $A$ function $f: A \rightarrow B$ is said to be a one - one function or injective mapping if different elements of $A$ have different $f$ images in $B$.
A function $f$ is injective if and only if whenever $f(x)=f(y), x=y$.
Example: $f(x)=x+9$ from the set of real number $R$ to $R$ is an injective function. When $x=3$, then : $f(x)=$ 12, when $f(y)=8$, the value of $y$ can only be 3, so $x=y$.
(ii) surjective function
Definition: If the function $\mathrm{f}: \mathrm{A} \rightarrow \mathrm{B}$ is such that each element in $\mathrm{B}$ (co - domain) is the ' $\mathrm{f}$ ' image of atleast one element in $A$, then we say that $f$ is a function of $A$ 'onto' $B$. Thus $f$ : $A \rightarrow B$ is surjective if, for all b $\in B$, there are some $a \in A$ such that $f(a)=b$.
Example: The function $f(x)=2 x$ from the set of natural numbers $N$ to the set of non negative even numbers is a surjective function.
(iii) bijective function
Definition: A function $f$ (from set $A$ to $B$ ) is bijective if, for every $y$ in $B$, there is exactly one $x$ in $A$ such that $f(x)=y .$ Alternatively, $f$ is bijective if it is a one - to - one correspondence between those sets, in other words, both injective and surjective.
Example: If $f(x)=x^{2}$, from the set of positive real numbers to positive real numbers is both injective and surjective.Thus it is a bijective function.
(iv)many - one function
Defintion : A function $\mathrm{f}: \mathrm{A} \rightarrow \mathrm{B}$ is said to be a many one functions if two or more elements of $\mathrm{A}$ have the same $\mathrm{f}$ image in $\mathrm{B}$.
trigonometric functions such as $\sin x$ are many - to - one since $\sin x=\sin (2 \pi+x)=\sin (4 \pi+x)$ and so one...
(v) into function
Definition: If $f: A \rightarrow B$ is such that there exists atleast one element in co - domain, which is not the image of any element in the domain, then $f(x)$ is into.
Let $f(x)=y=x-1000$
$\Rightarrow x=y+1000=g(y)$ (say)
Here $g(y)$ is defined for each $y \in I$, but $g(y) \notin N$ for $y \leq-1000 .$ Hence, $f$ is into.
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All Study Material
- JEE Main
- Exam Pattern
- Previous Year Papers
- PYQ Chapterwise
- Physics
- Kinematics 1D
- Kinemetics 2D
- Friction
- Work, Power, Energy
- Centre of Mass and Collision
- Rotational Dynamics
- Gravitation
- Calorimetry
- Elasticity
- Thermal Expansion
- Heat Transfer
- Kinetic Theory of Gases
- Thermodynamics
- Simple Harmonic Motion
- Wave on String
- Sound waves
- Fluid Mechanics
- Electrostatics
- Current Electricity
- Capacitor
- Magnetism and Matter
- Electromagnetic Induction
- Atomic Structure
- Dual Nature of Matter
- Nuclear Physics
- Radioactivity
- Semiconductors
- Communication System
- Error in Measurement & instruments
- Alternating Current
- Electromagnetic Waves
- Wave Optics
- X-Rays
- All Subjects
- Physics
- Motion in a Plane
- Law of Motion
- Work, Energy and Power
- Systems of Particles and Rotational Motion
- Gravitation
- Mechanical Properties of Solids
- Mechanical Properties of Fluids
- Thermal Properties of matter
- Thermodynamics
- Kinetic Theory
- Oscillations
- Waves
- Electric Charge and Fields
- Electrostatic Potential and Capacitance
- Current Electricity
- Thermoelectric Effects of Electric Current
- Heating Effects of Electric Current
- Moving Charges and Magnetism
- Magnetism and Matter
- Electromagnetic Induction
- Alternating Current
- Electromagnetic Wave
- Ray Optics and Optical Instruments
- Wave Optics
- Dual Nature of Radiation and Matter
- Atoms
- Nuclei
- Semiconductor Electronics: Materials, Devices and Simple Circuits.
- Chemical Effects of Electric Current,