Q 1 :

Let P={θ:sinθ-cosθ=2cosθ} and Q={θ:sinθ+cosθ=2sinθ} be two sets. Then            [2011]

  • P⊂Q and Q-P≠ϕ   

     

  • Q⊄P   

     

  • P⊄Q   

     

  • P=Q

     

(4)

P={θ:sinθ-cosθ=2cosθ}

⇒sinθ=(2+1)cosθ⇒tanθ=2+1

Now, Q={θ:sinθ+cosθ=2sinθ}

⇒cosθ=(2-1)sinθ⇒tanθ=12-1×2+12+1

⇒tanθ=2+1

∴ P=Q



Q 2 :

Let S = {1, 2, 3, 4}. The total number of unordered pairs of disjoint subsets of S is equal to            [2010]

  • 25

     

  • 34

     

  • 42

     

  • 41

     

(4)

S={1,2,3,4}

Let A and B be disjoint subsets of S

Now for any element a∈S, it has three possibilities: either it is in A or B or none

⇒For every element out of 4 elements there are three choices

∴ Total options=34=81

Here A≠B except when A=B=ϕ

∴ 81-1=80 ordered pairs (A,B) are there for which A≠B

Hence total number of unordered pairs of disjoint subsets=802+1=41