🛠️ JEE➗ Maths

Define a relation \(R\) on the interval \(\left[0, \frac{\pi}{2}\right)\) by \(x R y\) if and only if \(\sec ^2 x-\tan ^…

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Define a relation \(R\) on the interval \(\left[0, \frac{\pi}{2}\right)\) by \(x R y\) if and only if \(\sec ^2 x-\tan ^2 y=1\). Then \(R\) is:

[JEE Main 2025, 29 Jan (Shift 1)]

a

an equivalence relation

b

both reflexive and transitive but not symmetric

c

both reflexive and symmetric but not transitive

d

reflexive but neither symmetric nor transitive

✓ Correct answer: a)

an equivalence relation

Explanation

Given \(x R y \Leftrightarrow \sec ^2 x-\tan ^2 y=1\)

Using \(\sec ^2 x-1=\tan ^2 x\), we get \(\tan ^2 x=\tan ^2 y\)

Since \(x, y \in\left[0, \frac{\pi}{2}\right)\),

we have \(\tan x \geq 0, \tan y \geq 0\), so \(\tan x=\tan y\)

Now \(\tan x\) is one-one on \(\left[0, \frac{\pi}{2}\right)\), hence \(x=y\)

So the relation becomes \(x R y \Longleftrightarrow x=y\)

Therefore \(R\) is reflexive, symmetric and transitive

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