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Q.Check whether the relation R in ℝ defined by R = {(a, b); a ≤ b³} is reflexive, symmetric or transitive.

Himachal HpboseHPBOSE Plus Two Board 2025Subjective· 3mImportance★★★★★
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RR fails all three properties — a single counterexample kills each one.

Reflexive: RR is reflexive if a≤a3a\le a^3 for every a∈Ra\in\mathbb{R}. Take a=12a=\dfrac12: is 12≤(12)3=18\dfrac12\le\left(\dfrac12\right)^3=\dfrac18? No, 12>18\dfrac12>\dfrac18. So (a,a)∉R(a,a)\notin R for this aa — RR is not reflexive.

Symmetric: RR is symmetric if a≤b3⇒b≤a3a\le b^3 \Rightarrow b\le a^3 for all a,ba,b. Take a=1, b=2a=1,\ b=2: 1≤23=81\le 2^3=8 is true, so (1,2)∈R(1,2)\in R. But is 2≤13=12\le 1^3=1? No. So (2,1)∉R(2,1)\notin R even though (1,2)∈R(1,2)\in R — RR is not symmetric.

Transitive: RR is transitive if a≤b3a\le b^3 and b≤c3b\le c^3 together imply a≤c3a\le c^3. Take a=10, b=3, c=2a=10,\ b=3,\ c=2: …

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