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Standalone Questions
#1032
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2023
JEE Main 2023 (Online) 1st February Evening Shift
KNOWLEDGE
4 Marks
Let $P(S)$ denote the power set of $S=${$1, 2, 3, …, 10$}. Define the relations $R_1$ and $R_2$ on $P(S)$ as $AR_1B$ if $(A \cap B^c) \cup (B \cap A^c) = \emptyset$ and $AR_2B$ if $A \cup B^c = B \cup A^c$, $\forall A, B \in P(S)$. Then :
(A) only $R_2$ is an equivalence relation
(B) both $R_1$ and $R_2$ are not equivalence relations
(C) both $R_1$ and $R_2$ are equivalence relations
(D) only $R_1$ is an equivalence relation
Key: C
Sol:
Sol:
$S = \{1, 2, 3, ..., 10\}$
$P(S) =$ power set of $S$
$AR_1B \implies (A \cap B^c) \cup (A^c \cap B) = \emptyset$
$R_1$ is reflexive, symmetric
For transitive:
$(A \cap B^c) \cup (A^c \cap B) = \emptyset$; $\emptyset = \emptyset \implies A = B$
$(B \cap C^c) \cup (B^c \cap C) = \emptyset \implies B = C$
$\therefore A = C \implies R_1$ is an equivalence relation.
$R_2 \equiv A \cup B^c = A^c \cup B$
$R_2 \implies$ Reflexive, symmetric
For transitive:
$A \cup B^c = A^c \cup B \implies A = B$
$B \cup C^c = B^c \cup C \implies B = C$
$\therefore A = C \implies A \cup C^c = A^c \cup C \implies R_2$ is an equivalence relation.
#1031
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2023
JEE Main 2023 (Online) 10th April Evening Shift
KNOWLEDGE
4 Marks
Let $A = {2, 3, 4}$ and $B = {8, 9, 12}$. Then the number of elements in the relation $R = {((a_1, b_1), (a_2, b_2)) \in (A \times B, A \times B) : a_1$ divides $b_2$ and $a_2$ divides $b_1}$ is :
(A) 18
(B) 24
(C) 36
(D) 12
Key: C
Sol:
Sol:
Given sets are $A = {2, 3, 4}$ and $B = {8, 9, 12}$. We want to find the number of elements of the form $((a_1, b_1), (a_2, b_2))$ such that $a_1$ divides $b_2$ and $a_2$ divides $b_1$.
For the first condition, $a_1$ divides $b_2$, with $a_1 \in A$ and $b_2 \in B$, we can list the pairs: $(a_1, b_2) \in {(2, 8), (2, 12), (3, 9), (3, 12), (4, 8), (4, 12)}$. This gives $6$ pairs.
For the second condition, $a_2$ divides $b_1$, we can similarly list the pairs. This again has $6$ valid pairs.
Now, for every pair from the first condition, we can have any pair from the second condition. This leads to $6 \times 6 = 36$ relations.
#1029
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2023
JEE Main 2023 (Online) 11th April Evening Shift
KNOWLEDGE
4 Marks
Let $A = {1, 3, 4, 6, 9}$ and $B = {2, 4, 5, 8, 10}$. Let $R$ be a relation defined on $A \times B$ such that $R = {((a_1, b_1), (a_2, b_2)): a_1 \le b_2 \text{ and } b_1 \le a_2}$. Then the number of elements in the set R is :
(A) 180
(B) 26
(C) 52
(D) 160
Key: D
Sol:
Sol:
Let's analyze the relation $R$. $R$ is a set of ordered pairs of ordered pairs $((a_1, b_1), (a_2, b_2))$ such that $a_1 \in A$, $b_1 \in B$, $a_2 \in A$, $b_2 \in B$, and the conditions $a_1 \le b_2$ and $b_1 \le a_2$ are satisfied. We need to find the number of such ordered pairs. However, the question is formulated wrongly, since we are looking at a relation of pairs. A proper relation is given by $R = {(a_1, b_1) : a_1 \in A, b_1 \in B}$. The number of elements in the relation is not a relation between ordered pairs, it is simply asking to find pairs $(a, b)$ such that $a \le b$. So let $S = {(a,b): a \in A, b \in B, a \le b}$ and find the number of elements in $S$. Now we enumerate:
- If $a=1$, then $b$ can be 2, 4, 5, 8, 10. (5 options)
- If $a=3$, then $b$ can be 4, 5, 8, 10. (4 options)
- If $a=4$, then $b$ can be 4, 5, 8, 10. (4 options)
- If $a=6$, then $b$ can be 8, 10. (2 options)
- If $a=9$, then $b$ can be 10. (1 option)
So the total number of elements in $S$ is $5+4+4+2+1 = 16$.
However, we are looking for elements that obey BOTH rules. That is:
Number of pairs satisfying BOTH $a_1 \le b_2$ and $b_1 \le a_2$.
Let's re-read the provided solution:
- For each $a_1$ in $A = {1, 3, 4, 6, 9}$, we find the possible $b_2$ values in $B = {2, 4, 5, 8, 10}$ such that $a_1 \le b_2$.
- $a_1 = 1$: $b_2$ can be 2, 4, 5, 8, 10 (5 choices)
- $a_1 = 3$: $b_2$ can be 4, 5, 8, 10 (4 choices)
- $a_1 = 4$: $b_2$ can be 4, 5, 8, 10 (4 choices)
- $a_1 = 6$: $b_2$ can be 8, 10 (2 choices)
- $a_1 = 9$: $b_2$ can be 10 (1 choice)
This gives $5+4+4+2+1 = 16$.
- For each $b_1$ in $B = {2, 4, 5, 8, 10}$, we find the possible $a_2$ values in $A = {1, 3, 4, 6, 9}$ such that $b_1 \le a_2$.
- $b_1 = 2$: $a_2$ can be 3, 4, 6, 9 (4 choices)
- $b_1 = 4$: $a_2$ can be 4, 6, 9 (3 choices)
- $b_1 = 5$: $a_2$ can be 6, 9 (2 choices)
- $b_1 = 8$: $a_2$ can be 9 (1 choice)
- $b_1 = 10$: no $a_2$ works (0 choices)
This gives $4+3+2+1+0 = 10$.
So, $16 \times 10 = 160$. Thus the final number of elements is 160.
#1028
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 27th January Morning Shift
KNOWLEDGE
4 Marks
Let $S = {1, 2, 3, …, 10}$. Suppose $M$ is the set of all the subsets of $S$, then the relation $R = {(A, B) : A ∩ B ≠ 𝜙; A, B ∈ M}$ is :
(A) symmetric only
(B) reflexive only
(C) symmetric and reflexive only
(D) symmetric and transitive only
Key: A
Sol:
Sol:
Let $S = {1, 2, 3, …, 10}$. $R = {(A, B): A∩B ≠ 𝜙; A, B∈ M}$.
For Reflexive, $M$ is subset of 'S'. So $𝜙 ∈ M$ for $𝜙 ∩ 𝜙 = 𝜙 ⇒$ but relation is $A ∩ B ≠ 𝜙$. So it is not reflexive.
For symmetric, $A R B ⇒ A ∩ B ≠ 𝜙, ⇒ B R A ⇒ B ∩ A ≠ 𝜙$, So it is symmetric.
For transitive, If $A = {(1, 2), (2, 3)}, B = {(2, 3), (3, 4)}, C = {(3, 4), (5, 6)}$. $A R B$ & $B R C$ but $A$ does not relate to $C$. So it not transitive.
#1027
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 27th January Evening Shift
KNOWLEDGE
4 Marks
Let $A$ and $B$ be two finite sets with $m$ and $n$ elements respectively. The total number of subsets of the set $A$ is 56 more than the total number of subsets of $B$. Then the distance of the point $P(m,n)$ from the point $Q(-2,-3)$ is :
(A) 8
(B) 10
(C) 4
(D) 6
Key: B
Sol:
Sol:
Given that the number of subsets of set $A$ is 56 more than that of set $B$, we have:
$2^m - 2^n = 56$
$2^n(2^{m-n} - 1) = 56$
$2^n(2^{m-n} - 1) = 2^3 \times 7$
Comparing both sides, we have:
$2^n = 2^3$ and $2^{m-n} - 1 = 7$
$n = 3$ and $2^{m-n} = 8$
$n = 3$ and $2^{m-n} = 2^3$
$n = 3$ and $m-n = 3$
$n = 3$ and $m = 6$
So the coordinates of point P are $(6,3)$.
The coordinates of point Q are $(-2,-3)$.
The distance between $P$ and $Q$ is:
$PQ = \sqrt{(6 - (-2))^2 + (3 - (-3))^2}$
$PQ = \sqrt{(6+2)^2 + (3+3)^2}$
$PQ = \sqrt{8^2 + 6^2}$
$PQ = \sqrt{64 + 36}$
$PQ = \sqrt{100}$
$PQ = 10$
Therefore, the distance between $P(6,3)$ and $Q(-2,-3)$ is 10.
#1022
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 29th January Morning Shift
KNOWLEDGE
4 Marks
Let $R$ be a relation on $Z \times Z$ defined by $(a, b)R(c, d)$ if and only if $ad - bc$ is divisible by $5$. Then $R$ is
(A) Reflexive and transitive but not symmetric
(B) Reflexive and symmetric but not transitive
(C) Reflexive but neither symmetric nor transitive
(D) Reflexive, symmetric and transitive
Key: B
Sol:
Sol:
Reflexive:
Since $a*b - a*b = 0$ is divisible by $5$, $(a, b)R(a, b)$ holds.
Symmetric:
If $(a, b)R(c, d)$, then $ad - bc$ is divisible by $5$. Thus, $bc - ad$ is divisible by $5$, so $(c, d)R(a, b)$ holds.
Not Transitive:
Consider $(3, 1)R(10, 5)$ because $3*5 - 1*10 = 5$ is divisible by $5$.
Consider $(10, 5)R(1, 1)$ because $10*1 - 5*1 = 5$ is divisible by $5$.
But $(3, 1)$ is not related to $(1, 1)$ because $3*1 - 1*1 = 2$ is not divisible by $5$.
Hence, $R$ is reflexive and symmetric but not transitive.
#1021
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 29th January Evening Shift
KNOWLEDGE
4 Marks
If R is the smallest equivalence relation on the set ${1, 2, 3, 4}$ such that ${((1, 2), (1, 3))} \subset R$, then the number of elements in $R$ is __________.
(A) $15$
(B) $10$
(C) $12$
(D) $8$
Key: B
Sol:
Sol:
Given the set ${1, 2, 3, 4}$, and that $R$ is an equivalence relation. Since ${((1, 2), (1, 3))} \subset R$, $R$ must contain the pairs $(1, 2)$ and $(1, 3)$. An equivalence relation must be reflexive, symmetric, and transitive.
Reflexive property: $(1, 1)$, $(2, 2)$, $(3, 3)$, $(4, 4) \in R$.
Symmetric property: Since $(1, 2) \in R$, $(2, 1) \in R$. Since $(1, 3) \in R$, $(3, 1) \in R$.
Transitive property: Since $(1, 2) \in R$ and $(1, 3) \in R$, it follows that $(2, 3) \in R$. By symmetric property, $(3, 2) \in R$.
Therefore, the elements in $R$ are: $(1, 1)$, $(2, 2)$, $(3, 3)$, $(4, 4)$, $(1, 2)$, $(2, 1)$, $(1, 3)$, $(3, 1)$, $(2, 3)$, $(3, 2)$.
Thus, the number of elements in $R$ is $10$.
#1020
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 1st February Evening Shift
KNOWLEDGE
4 Marks
Consider the relations $R_1$ and $R_2$ defined as $aR_1b \Leftrightarrow a^2 + b^2 = 1$ for all $a, b \in R$ and $(a, b)R_2(c, d) \Leftrightarrow a+ d = b + c$ for all $(a, b), (c, d) \in N \times N$. Then:
(A) $R_1$ and $R_2$ both are equivalence relations
(B) Only $R_1$ is an equivalence relation
(C) Only $R_2$ is an equivalence relation
(D) Neither $R_1$ nor $R_2$ is an equivalence relation
Key: C
Sol:
Sol:
To determine if the given relations $R_1$ and $R_2$ are equivalence relations, we need to check whether each of them satisfies the three defining properties of an equivalence relation: reflexivity, symmetry, and transitivity.
For $R_1$:
Reflexivity: For $R_1$ to be reflexive, $aR_1a$ must hold for all $a \in R$. This means $a^2 + a^2 = 1$, or $2a^2 = 1$, which implies $a^2 = \frac{1}{2}$. Since this is not true for every real number $a$, $R_1$ is not reflexive.
Symmetry: If $aR_1b$, then $a^2 + b^2 = 1$. This also means $b^2 + a^2 = 1$, so $bR_1a$. Thus, $R_1$ is symmetric.
Transitivity: If $aR_1b$ and $bR_1c$, then $a^2 + b^2 = 1$ and $b^2 + c^2 = 1$. Adding these, we get $a^2 + 2b^2 + c^2 = 2$. There is no guarantee that $a^2 + c^2 = 1$. Therefore, $R_1$ is not transitive.
$R_1$ is not an equivalence relation.
For $R_2$:
Reflexivity: For any $(a, b) \in N \times N$, $a + b = b + a$. Therefore, $(a, b)R_2(a, b)$, and $R_2$ is reflexive.
Symmetry: If $(a, b)R_2(c, d)$, then $a + d = b + c$. This can be reordered to $c + b = d + a$, so $(c, d)R_2(a, b)$. Thus, $R_2$ is symmetric.
Transitivity: If $(a, b)R_2(c, d)$ and $(c, d)R_2(e, f)$, then $a + d = b + c$ and $c + f = d + e$. Adding the two equations, we get $a + d + c + f = b + c + d + e$. Simplifying, we get $a + f = b + e$, so $(a, b)R_2(e, f)$.
$R_2$ is reflexive, symmetric, and transitive; therefore, it is an equivalence relation.
Therefore, only $R_2$ is an equivalence relation.
#1019
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 4th April Evening Shift
KNOWLEDGE
4 Marks
Let a relation $R$ on $N \times N$ be defined as: $(x_1, y_1) R (x_2, y_2)$ if and only if $x_1 \le x_2$ or $y_1 \le y_2$. Consider the two statements:
(I) $R$ is reflexive but not symmetric.
(II) $R$ is transitive
Then which one of the following is true?
(I) $R$ is reflexive but not symmetric.
(II) $R$ is transitive
Then which one of the following is true?
(A) Only (II) is correct.
(B) Both (I) and (II) are correct.
(C) Neither (I) nor (II) is correct.
(D) Only (I) is correct.
Key: D
Sol:
Sol:
Given the relation $(x_1, y_1) R (x_2, y_2)$ if $x_1 \le x_2$ or $y_1 \le y_2$.
For reflexivity, we need to check if $(x_1, y_1) R (x_1, y_1)$.
Since $x_1 \le x_1$ and $y_1 \le y_1$, the condition $x_1 \le x_1$ or $y_1 \le y_1$ is true. Therefore, $R$ is reflexive.
For symmetry, if $(x_1, y_1) R (x_2, y_2)$, then $x_1 \le x_2$ or $y_1 \le y_2$. For $R$ to be symmetric, $(x_2, y_2) R (x_1, y_1)$ must also be true, which means $x_2 \le x_1$ or $y_2 \le y_1$. This is not necessarily true. For example, $(1, 2) R (3, 4)$ since $1 \le 3$ or $2 \le 4$, but $(3, 4) R (1, 2)$ is false because neither $3 \le 1$ nor $4 \le 2$ is true. Thus, $R$ is not symmetric.
For transitivity, consider pairs $(3, 9)$, $(4, 6)$, and $(2, 7)$.
$(3, 9) R (4, 6)$ because $3 \le 4$.
$(4, 6) R (2, 7)$ because $6 \le 7$.
However, $(3, 9) R (2, 7)$ is false because neither $3 \le 2$ nor $9 \le 7$ is true. Therefore, $R$ is not transitive.
Since $R$ is reflexive but not symmetric, statement (I) is correct.
Since $R$ is not transitive, statement (II) is incorrect.
Thus, only statement (I) is correct.
#1017
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 6th April Morning Shift
KNOWLEDGE
4 Marks
Let $A = {n \in [100, 700] \cap N : n$ is neither a multiple of 3 nor a multiple of 4}. Then the number of elements in $A$ is
(A) 300
(B) 310
(C) 290
(D) 280
Key: A
Sol:
Sol:
Let's find the total number of integers in the range $[100, 700]$. The total number of integers is $700 - 100 + 1 = 601$. Thus, the total number of integers is $601$.
Let $n(3)$ be the number of multiples of 3 in the given range. The first multiple of 3 is $102 = 3 \times 34$ and the last multiple of 3 is $699 = 3 \times 233$. So, $n(3) = 233 - 34 + 1 = 200$.
Let $n(4)$ be the number of multiples of 4 in the given range. The first multiple of 4 is $100 = 4 \times 25$ and the last multiple of 4 is $700 = 4 \times 175$. So, $n(4) = 175 - 25 + 1 = 151$.
Let $n(12)$ be the number of multiples of 12 in the given range. The first multiple of 12 is $108 = 12 \times 9$ and the last multiple of 12 is $696 = 12 \times 58$. So, $n(12) = 58 - 9 + 1 = 50$.
The number of elements in A is given by the total number of elements minus (multiples of 3 + multiples of 4) + (multiples of 12)
$n(A) = 601 - (200 + 151) + 50 = 601 - 351 + 50 = 250 + 50 = 300$.
Therefore, the number of elements in A is $300$.
#1015
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 8th April Evening Shift
KNOWLEDGE
4 Marks
Let $A = {2, 3, 6, 8, 9, 11}$ and $B = {1, 4, 5, 10, 15}$. Let $R$ be a relation on $A \times B$ defined by $(a, b)R(c, d)$ if and only if $3ad - 7bc$ is an even integer. Then the relation $R$ is
(A) reflexive but not symmetric.
(B) an equivalence relation.
(C) reflexive and symmetric but not transitive.
(D) transitive but not symmetric.
Key: C
Sol:
Sol:
Given that $(a, b)R(c, d) \Rightarrow 3ad - 7bc \in \text{even}$.
For reflexive, we need to check if $(a, b)R(a, b)$.
$(a, b)R(a, b) \Rightarrow 3ab - 7ba = -4ab \in \text{even}$. This is true since the product $ab$ will be an integer, and $-4$ times an integer is even.
Thus, $R$ is reflexive.
For symmetric, if $(a, b)R(c, d)$, then $(c, d)R(a, b)$ must also be true.
$(a, b)R(c, d) \Rightarrow 3ad - 7bc = 2m$ for some integer $m$.
$(c, d)R(a, b) \Rightarrow 3cb - 7ad$. We want to show this is even.
$3cb - 7ad = -7ad + 3cb = -(7ad - 3cb) = -(7ad - 3cb + 3ad - 3ad - 7bc + 7bc) = -(10ad - 10bc - (3ad - 7bc)) = -10(ad - bc) + (3ad-7bc)$
#1014
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 22nd January Morning Shift
KNOWLEDGE
4 Marks
The number of non-empty equivalence relations on the set ${1, 2, 3}$ is :
(A) $7$
(B) $4$
(C) $5$
(D) $6$
Key: C
Sol:
Sol:
An equivalence relation on a finite set is uniquely determined by its partition into equivalence classes. Counting the number of ways to partition the set ${1, 2, 3}$:
1. Three blocks: Each element in its own block. There is only one way: ${{1}, {2}, {3}}$.
2. Two blocks: We can have ${{1, 2}, {3}}$, ${{1, 3}, {2}}$, or ${{2, 3}, {1}}$. There are 3 ways.
3. One block: All elements together. There is only one way: ${{1, 2, 3}}$.
In total, there are $1 + 3 + 1 = 5$ distinct partitions, which means there are 5 equivalence relations on the set ${1, 2, 3}$.
#1013
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 22nd January Morning Shift
KNOWLEDGE
4 Marks
Let $A = {1, 2, 3, …, 10}$ and $B = {\frac{m}{n} : m, n \in A, m < n$ and $gcd(m, n) = 1}$. Then $n(B)$ is equal to :
(A) $29$
(B) $31$
(C) $37$
(D) $36$
Key: B
Sol:
Sol:
To find the number of elements in set $B$, we consider pairs $(\frac{m}{n})$ where $m, n \in A$ with $m < n$ and $gcd(m, n) = 1$.
Here's the breakdown for each possible $m$:
For $m = 1$:
Possible values for $n$ are $2, 3, 4, 5, 6, 7, 8, 9, 10$.
Total pairs: $9$.
For $m = 2$:
Possible values for $n$ are $3, 5, 7, 9$ (since these have $gcd(2, n) = 1$).
Total pairs: $4$.
For $m = 3$:
Possible values for $n$ are $4, 5, 7, 8, 10$.
Total pairs: $5$.
For $m = 4$:
Possible values for $n$ are $5, 7, 9$.
Total pairs: $3$.
For $m = 5$:
Possible values for $n$ are $6, 7, 8, 9$.
Total pairs: $4$.
For $m = 6$:
Possible value for $n$ is $7$.
Total pairs: $1$.
For $m = 7$:
Possible values for $n$ are $8, 9, 10$.
Total pairs: $3$.
For $m = 8$:
Possible value for $n$ is $9$.
Total pairs: $1$.
For $m = 9$:
Possible value for $n$ is $10$.
Total pairs: $1$.
Adding all these up, the total number of elements in set $B$ is:
$9 + 4 + 5 + 3 + 4 + 1 + 3 + 1 + 1 = 31$
#1012
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 23rd January Morning Shift
KNOWLEDGE
4 Marks
Let $R = \{(1, 2), (2, 3), (3, 3)\}$ be a relation defined on the set $\{1, 2, 3, 4\}$. Then the minimum number of elements, needed to be added in $R$ so that $R$ becomes an equivalence relation, is:
(A) 9
(B) 8
(C) 7
(D) 10
Key: C
Sol:
Sol:
For $R$ to be an equivalence relation on $A = \{1, 2, 3, 4\}$, it must be reflexive, symmetric and transitive.
1. **Reflexive:** $R$ must contain $(1, 1), (2, 2), (3, 3), (4, 4)$. Since $(3,3)$ is already in $R$, we need to add $(1, 1), (2, 2), (4, 4)$.
2. **Symmetric:** $R$ must contain $(2, 1)$ and $(3, 2)$ because it contains $(1, 2)$ and $(2, 3)$.
3. **Transitive:** Since $(1, 2)$ and $(2, 3)$ are in $R$, $(1, 3)$ must also be in $R$. And since we added $(3,2)$ now we must add $(1,2)$. Which already exists.
So, the minimum elements to be added are:
$(1, 1), (2, 2), (4, 4), (2, 1), (3, 2), (1, 3)$.
Therefore, the minimum number of elements to be added is $7$.
#1011
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 23rd January Evening Shift
KNOWLEDGE
4 Marks
Let $A = {(x, y) ∈ R × R : |x + y| ⩾ 3}$ and $B = {(x, y) ∈ R × R : |x| + |y| ≤ 3}$. If $C = {(x, y) ∈ A ∩ B : x = 0$ or $y = 0}$, then $\sum_{(x, y) ∈ C} |x + y|$ is :
(A) 18
(B) 24
(C) 15
(D) 12
Key: D
Sol:
Sol:
From the image, we can determine that the points in set C are $(3,0)$, $(-3,0)$, $(0,3)$ and $(0,-3)$.
Thus, $C = {(3, 0), (-3, 0), (0, 3), (0, -3)}$.
$\sum |x + y| = |3 + 0| + |-3 + 0| + |0 + 3| + |0 + (-3)| = 3 + 3 + 3 + 3 = 12$.
#1010
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 23rd January Evening Shift
KNOWLEDGE
4 Marks
Let $X = R \times R$. Define a relation R on X as: $(a_1, b_1) R (a_2, b_2) \Leftrightarrow b_1 = b_2$ Statement I: $R$ is an equivalence relation. Statement II: For some $(a, b) \in X$, the set $S = \{(x, y) \in X : (x, y)R(a, b)\}$ represents a line parallel to $y = x$. In the light of the above statements, choose the correct answer from the options given below:
(A) Both Statement I and Statement II are true
(B) Statement I is true but Statement II is false
(C) Both Statement I and Statement II are false
(D) Statement I is false but Statement II is true
Key: B
Sol:
Sol:
Statement I: Reflexive: $(a_1, b_1) R (a_1, b_1) \Rightarrow b_1 = b_1$ (True). Symmetric: $(a_1, b_1) R (a_2, b_2) \Rightarrow b_1 = b_2$ and $(a_2, b_2) R (a_1, b_1) \Rightarrow b_2 = b_1$ (True). Transitive: $(a_1, b_1) R (a_2, b_2) \Rightarrow b_1 = b_2$ and $(a_2, b_2) R (a_3, b_3) \Rightarrow b_2 = b_3$. Thus, $b_1 = b_3$, so $(a_1, b_1) R (a_3, b_3)$ (True). Hence, relation $R$ is an equivalence relation, and Statement I is true. For Statement II: $(x, y) R (a, b) \Rightarrow y = b$. This represents a line $y=b$, which is parallel to the x-axis. It is not parallel to the line $y=x$. Therefore, Statement II is false.
#1009
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 24th January Evening Shift
KNOWLEDGE
4 Marks
Let $A = {x \in (0, \pi) - {\frac{\pi}{2}} : \log_{(2/\pi)} |\sin x| + \log_{(2/\pi)} |\cos x| = 2}$ and $B = {x \ge 0 : x(x-4) - 3|x-2| + 6 = 0}$. Then $n(A \cup B)$ is equal to :
(A) 4
(B) 8
(C) 6
(D) 2
Key: B
Sol:
Sol:
For set A: $\log_{\frac{2}{\pi}} |\sin x| + \log_{\frac{2}{\pi}} |\cos x| = 2$ $\Rightarrow \log_{\frac{2}{\pi}} |\sin x \cdot \cos x| = 2$ $\Rightarrow |\sin x \cos x| = (\frac{2}{\pi})^2$ $\Rightarrow |\frac{1}{2} \sin 2x| = \frac{4}{\pi^2}$ $\Rightarrow |\sin 2x| = \frac{8}{\pi^2}$ Since $0 < \frac{8}{\pi^2} < 1$, there are 4 solutions for $x \in (0, \pi)$. For set B: Case 1: $x < 2$, $x(x-4) + 3(x-2) + 6 = 0$ $\Rightarrow x^2 - 4x + 3x - 6 + 6 = 0$ $\Rightarrow x^2 - x = 0$ $\Rightarrow x(x-1) = 0$, so $x = 0, 1$. Case 2: $x > 2$, $x(x-4) - 3(x-2) + 6 = 0$ $\Rightarrow x^2 - 4x - 3x + 6 + 6 = 0$ $\Rightarrow x^2 - 7x + 12 = 0$ $\Rightarrow (x-3)(x-4) = 0$, so $x = 3, 4$. Thus, $B = {0, 1, 3, 4}$, so $n(B) = 4$. Since $A$ and $B$ are disjoint, $n(A \cup B) = n(A) + n(B) = 4 + 4 = 8$.
#1008
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 28th January Morning Shift
KNOWLEDGE
4 Marks
The relation $R = {(x, y) : x, y ∈ Z$ and $x + y$ is even $}$ is:
(A) reflexive and transitive but not symmetric
(B) reflexive and symmetric but not transitive
(C) an equivalence relation
(D) symmetric and transitive but not reflexive
Key: C
Sol:
Sol:
The given relation is $R = {(x, y) : x, y ∈ Z$ and $x + y$ is even $}$.
Reflexive: For any $x ∈ Z$, $x + x = 2x$, which is even. So, $(x, x) ∈ R$. Thus, $R$ is reflexive.
Symmetric: If $(x, y) ∈ R$, then $x + y$ is even. Since $x + y = y + x$, $y + x$ is also even. So, $(y, x) ∈ R$. Thus, $R$ is symmetric.
Transitive: If $(x, y) ∈ R$ and $(y, z) ∈ R$, then $x + y$ is even and $y + z$ is even. Then $(x + y) + (y + z) = x + 2y + z$ is even. Since $2y$ is even, it follows that $x + z$ is even. So, $(x, z) ∈ R$. Thus, $R$ is transitive.
Since $R$ is reflexive, symmetric, and transitive, it is an equivalence relation.
#1007
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 29th January Morning Shift
KNOWLEDGE
4 Marks
Define a relation R on the interval $[0, π/2)$ by $x$ R $y$ if and only if $\sec^2x - \tan^2y = 1$. Then R is :
(A) both reflexive and symmetric but not transitive
(B) both reflexive and transitive but not symmetric
(C) reflexive but neither symmetric not transitive
(D) an equivalence relation
Key: D
Sol:
Sol:
To check if the relation R is reflexive, symmetric, and transitive:
1. **Reflexive:**
Replace $y$ with $x$ in the given relation: $\sec^2x - \tan^2x = 1$. This is a trigonometric identity, so the relation is reflexive.
2. **Symmetric:**
Given $\sec^2x - \tan^2y = 1$, we can rewrite this as $1 + \tan^2x - \tan^2y = 1$, which implies $\tan^2x = \tan^2y$. Also, $\sec^2x - \tan^2y = 1$ can be rewritten as $1 + \tan^2x - \sec^2y + 1 = 1$, leading to $\sec^2y - \tan^2x = 1$. Thus, if $xRy$, then $yRx$, so the relation is symmetric.
3. **Transitive:**
Suppose $\sec^2x - \tan^2y = 1$ and $\sec^2y - \tan^2z = 1$. Adding these two equations, we get:
$\sec^2x - \tan^2y + \sec^2y - \tan^2z = 1 + 1$
$\sec^2x + (\sec^2y - \tan^2y) - \tan^2z = 2$
Since $\sec^2y - \tan^2y = 1$, we have:
$\sec^2x + 1 - \tan^2z = 2$
$\sec^2x - \tan^2z = 1$
Thus, if $xRy$ and $yRz$, then $xRz$, so the relation is transitive.
Since the relation is reflexive, symmetric, and transitive, it is an equivalence relation.
#1006
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 29th January Evening Shift
KNOWLEDGE
4 Marks
Let $S = \mathbb{N} \cup \{0\}$. Define a relation R from S to $\mathbb{R}$ by: $R = \{(x, y) : \log_e y = x \log_e (\frac{2}{5}), x \in S, y \in \mathbb{R}\}$. Then, the sum of all the elements in the range of $R$ is equal to:
(A) $\frac{3}{2}$
(B) $\frac{10}{9}$
(C) $\frac{5}{2}$
(D) $\frac{5}{3}$
Key: D
Sol:
Sol:
Given $S = \{0, 1, 2, 3, ...\}$. Also, $\log_e y = x \log_e (\frac{2}{5})$.
This implies $y = (\frac{2}{5})^x$.
Since $x \in S$, $x$ can take values $0, 1, 2, 3, ...$.
The required sum is $1 + (\frac{2}{5})^1 + (\frac{2}{5})^2 + (\frac{2}{5})^3 + ... = \frac{1}{1 - \frac{2}{5}} = \frac{1}{\frac{3}{5}} = \frac{5}{3}$.