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
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
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