Let \(A=\{-3,-2,-1,0,1,2,3\}\). Let \(R\) be a relation on \(A\) defined by \(x R y\) if and only if \(0 \leq x^2+2 y \l…
Let \(A=\{-3,-2,-1,0,1,2,3\}\). Let \(R\) be a relation on \(A\) defined by \(x R y\) if and only if \(0 \leq x^2+2 y \leq 4\). Let \(l\) be the number of elements in \(R\) and \(m\) be the minimum number of elements required to be added in \(R\) to make it a reflexive relation, then \(l+m\) is equal to
[JEE Main 2025, 3 Apr (Shift 1)]
\(18\)
\(A=\{-3,-2,-1,0,1,2,3\}, x R y \Longleftrightarrow 0 \leq x^2+2 y \leq 4, l=|R| \)
\(x= \pm 3, x^2=9: 0 \leq 9+2 y \leq 4 \Rightarrow-9 \leq 2 y \leq-5\)
\(\Rightarrow y=-3 \Rightarrow 2 \) pairs
\(x= \pm 2, x^2=4: 0 \leq 4+2 y \leq 4 \Rightarrow-4 \leq 2 y \leq 0\)
\(\Rightarrow y \in\{-2,-1,0\} \Rightarrow 6 \) pairs
\(x= \pm 1, x^2=1: 0 \leq 1+2 y \leq 4 \Rightarrow-1 \leq 2 y \leq 3\)
\(\Rightarrow y \in\{0,1\} \Rightarrow 4\) pairs
\(x=0, x^2=0: 0 \leq 2 y \leq 4\)
\(\Rightarrow y \in\{0,1,2\} \Rightarrow 3\) pairs
\( l=2+6+4+3=15\)
Reflexive on \(A\) means \((a, a) \in R \ \forall a \in A\), i.e. \(0 \leq a^2+2 a \leq 4\)
\(a=-3,-2,0,1\) satisfy it; \(a=-1,2,3\) do not satisfy it \(\Rightarrow m=3\)
\(l+m=15+3=18\)
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