1.

Mark the tick against the correct answer in the following: Let S be the set of all real numbers and let R be a relation on S defined by a R b ⇔ |a| ≤ b. Then, R is A. reflexive but neither symmetric nor transitive B. symmetric but neither reflexive nor transitive C. transitive but neither reflexive nor symmetric D. none of these

Answer»

Correct Answer is (C) transitive but neither reflexive nor symmetric

Given set S = {…….,-2,-1,0,1,2 …..}

And R = {(a, b) : a,b ∈ S and |a| ≤ b }

Formula

For a relation R in set A

Reflexive

The relation is reflexive if (a , a) ∈ R for every a ∈ A

Symmetric

The relation is Symmetric if (a , b) ∈ R , then (b , a) ∈ R

Transitive

Relation is Transitive if (a , b) ∈ R & (b , c) ∈ R , then (a , c) ∈ R

Equivalence

If the relation is reflexive , symmetric and transitive , it is an equivalence relation.

Check for reflexive

Consider , (a,a)

∴ |a| ≤ a and which is not always true.

Ex_if a=-2

∴ |-2| ≤ -2 ⇒ 2 ≤ -2 which is false

Therefore , R is not reflexive ……. (1)

Check for symmetric

a R b ⇒ |a| ≤ b

b R a ⇒ |b| ≤ a

Both cannot be true.

Ex _ If a=-2 and b=-1

∴ 2 ≤ -1 is false and 1 ≤ -2 which is also false

Therefore , R is not symmetric ……. (2)

Check for transitive

a R b ⇒ |a| ≤ b

a R b ⇒ |a| ≤ b

∴ |a| ≤ c

Ex _a=-5 , b= 7 and c=9

∴ 5 ≤ 7 , 7 ≤ 9 and hence 5 ≤ 9

Therefore , R is transitive ……. (3)

Now , according to the equations (1) , (2) , (3)

Correct option will be (C)



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