Class JEE Mathematics Sets, Relations, and Functions Q #1019
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4 Marks 2024 JEE Main 2024 (Online) 4th April Evening Shift MCQ SINGLE
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?
(A) Only (II) is correct.
(B) Both (I) and (II) are correct.
(C) Neither (I) nor (II) is correct.
(D) Only (I) is correct.
Correct Answer: D
Explanation
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.