Q.

If R is a relation defined by aRb iff a≤b on N×N, then which of the following is correct

1 R is not a symmetric relation  
2 R is a symmetric relation  
3 R is not a reflexive relation  
4 R is a equivalence relation  

Ans.

(1)

Now

limx→0α(1+x+x22!+x33!+⋯)+β(1-x+x22!-x33!+⋯)+γ(x-x33!+⋯)x3   [∵sinx≤x ∀x∈R]

Constant terms should be zero ⇒α+β=0

Coefficient of x should be zero ⇒α-β+γ=0

Coefficient of x2 should be zero limx→0x3(α3!-β3!-γ3!)+x4(α3!-β3!-γ3!)x3=23

⇒α2+β2=0,  Now ⇒α6-β6-γ6=23

⇒α=1, β=-1, γ=-2