Class JEE Mathematics Sets, Relations, and Functions Q #1071
KNOWLEDGE BASED
APPLY
4 Marks 2011 AIEEE MCQ SINGLE
Let $R$ be the set of real numbers. Statement I: $A = \{(x, y) \in R \times R: y - x \text{ is an integer }\}$ is an equivalence relation on $R$. Statement II: $B = \{(x,y) \in R \times R: x = \alpha y \text{ for some rational number } \alpha\}$ is an equivalence relation on $R$.
(A) Statement I is true, Statement II is true; Statement II is not a correct explanation for Statement I.
(B) Statement I is true, Statement II is false.
(C) Statement I is false, Statement II is true.
(D) Statement I is true, Statement II is true; Statement II is a correct explanation for Statement I.
Correct Answer: B
Explanation
Statement I: $A = \{(x, y) \in R \times R: y - x \text{ is an integer }\}$. Reflexivity: For all $x \in R$, $x - x = 0$ which is an integer. Symmetry: For all $x, y \in R$, if $y - x$ is an integer, then $x - y = -(y - x)$ is also an integer. Transitivity: For all $x, y, z \in R$, if $y - x$ and $z - y$ are integers, then $(z - y) + (y - x) = z - x$ is also an integer. Therefore, $A$ is an equivalence relation on $R$. Statement II: $B = \{(x,y) \in R \times R: x = \alpha y \text{ for some rational number } \alpha\}$. Reflexivity: For all $x \in R$, $x = 1 \cdot x$. Since $1$ is a rational number, every element is related to itself. Symmetry: For all $x, y \in R$, if $x = \alpha y$ for some rational $\alpha$, then $y = \frac{1}{\alpha} x$. However, if $\alpha = 0$, then $\frac{1}{\alpha}$ is undefined, and therefore, $B$ doesn't satisfy symmetry. Transitivity: If $x = \alpha y$ and $y = \beta z$ for some rational numbers $\alpha$ and $\beta$, then $x = (\alpha \beta) z$. Since the product of rational numbers is rational, if $x$ is related to $y$ and $y$ is related to $z$, then $x$ is related to $z$. Therefore, $B$ is not an equivalence relation on $R$ since it does not satisfy the symmetry property. In conclusion, Statement I is true, and Statement II is false.

More from this Chapter

NUMERICAL
Let $\mathrm{A}=\{-4,-3,-2,0,1,3,4\}$ and $\mathrm{R}=\left\{(a, b) \in \mathrm{A} \times \mathrm{A}: b=|a|\right.$ or $\left.b^{2}=a+1\right\}$ be a relation on $\mathrm{A}$. Then the minimum number of elements, that must be added to the relation $\mathrm{R}$ so that it becomes reflexive and symmetric, is __________
NUMERICAL
In a survey of 220 students of a higher secondary school, it was found that at least 125 and at most 130 students studied Mathematics; at least 85 and at most 95 studied Physics; at least 75 and at most 90 studied Chemistry; 30 studied both Physics and Chemistry; 50 studied both Chemistry and Mathematics; 40 studied both Mathematics and Physics and 10 studied none of these subjects. Let $m$ and $n$ respectively be the least and the most number of students who studied all the three subjects. Then $\mathrm{m}+\mathrm{n}$ is equal to ___________.
MCQ_SINGLE
Let $R = \{(3, 3), (6, 6), (9, 9), (12, 12), (6, 12), (3, 9), (3, 12), (3, 6)\}$ be a relation on the set $A = \{3, 6, 9, 12\}$. The relation is :
NUMERICAL
Let $A=\{0,3,4,6,7,8,9,10\}$ and $R$ be the relation defined on $A$ such that $R=\{(x, y) \in A \times A: x-y$ is odd positive integer or $x-y=2\}$. The minimum number of elements that must be added to the relation $R$, so that it is a symmetric relation, is equal to ____________.
NUMERICAL
Let $A=\{1,2,3,4,5,6,7\}$. Define $B=\{T \subseteq A$ : either $1 \notin T$ or $2 \in T\}$ and $C=\{T \subseteq A: T$ the sum of all the elements of $T$ is a prime number $\}$. Then the number of elements in the set $B \cup C$ is ________________.
View All Questions