Show that the relation R in the set R of real numbers, defined a

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 Multiple Choice QuestionsShort Answer Type

211. Show that the relation R in R defined as R = {(a, b) : a ≤ b}, is reflexive and transitive but not symmetric.
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212. Show that the relation R in the set R of real numbers, defined as R = {(a, b) : a ≤ b2] is neither reflexive nor symmetric nor transitive.


R = {(a, b) : a ≤ b2}
(i) Since (a, a) ∉ R

open square brackets Take space straight a equals 1 third space then space 1 third greater than open parentheses 1 third close parentheses squared close square brackets

∴ R is not reflexive.
(ii) Also (a, b) ∈ R ⇏ (b, a) ∈ R
[Take a = 2 ,b = 6, then 2 ≤ 62 but (6)2 < 2 is not true]
∴ R is not symmetric.
(iii) Now (a, b), (b, c) ∈ R ∉ (a, c) ∈ R
[Take a = 1, b = – 2, c = – 3 ∴ a ≤ b2 . b ≤ c2 but a ≤ c2 is not true) ∴ R is not transitive.

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213. Check whether the relation R in R defined by R = {(a,b) : a ≤ b3} is refleive, symmetric or transitive.
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214. If R and R’ arc reflexive relations on a set then so are R ∪ R’ and R ∩ R’. 
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215. If R and R’ are symmetric relations on a set A, then R ∩ R’ is also a sysmetric relation on A.
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216. Show that the union of two symmetric relations on a set is again a symmetric relation on that set.
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217. Let A = {1. 2. 3}. Then show that the number of relations containing (1,2) and (2. 3) which are reflexive and transitive but not symmetric is four.
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218. Let X = {1, 2, 3, 4, 5, 6, 7, 8, 9}. Let R1 be a relation in X given by R1 = {(x, y) : x – y is divisible by 3} and R2 be another relation on X given by R2 = {(x, y) : {x, y} ⊂ {1,4, 7 }} or ⊂ {2, 5, 8} or {x, y,}⊂ {3, 6, 9}}. Show that R1 = R2.
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219.

Let R be the relation in the set N given by R = {(a, b) : a = b – 2, b > 6}.
Choose the correct answer.
(A) (2. 4) ∈ R (B) (3, 8) ∈ R (C) (6,8) ∈ R (D)(8,7) ∈ R 

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220.

Let A = {1, 2, 3}. Then number of relations containing (1, 2) and (1, 3) which are reflexive and symmetric but not transitive is

(A) 1    (B) 2    (C) 3    (D) 4

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