Q.

Define a relation R on the interval [0,π2) by xRy if and only if sec2xtan2y=1. Then R is :          [2025]

1 an equivalence relation.  
2 reflexive but neither symmetric not transitive.  
3 both reflexive and symmetric but not transitive.  
4 both reflexive and transitive but not symmetric.  

Ans.

(1)

sec2xtan2x=1, x[0,π2)

   R is reflexive

Consider, sec2xtan2y=1

 1+tan2x(sec2y1)=1

 1+tan2xsec2y+1=1  sec2ytan2x=1

   R is symmetric.

Now, if sec2xtan2y=1 and sec2ytan2z=1

Adding both equation, sec2xtan2y+sec2ytan2z=2

 sec2xtan2z=1        [ sec2ytan2y=1]

   R is transitive

Thus R is an equivalence relation.