Q 1 :

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

  • PQ and Q-Pϕ   

     

  • QP   

     

  • PQ   

     

  • P=Q

     

(4)

P={θ:sinθ-cosθ=2cosθ}

sinθ=(2+1)cosθtanθ=2+1

Now, Q={θ:sinθ+cosθ=2sinθ}

cosθ=(2-1)sinθtanθ=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 aS, 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 AB except when A=B=ϕ

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

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