Question
Question: If [cos<sup>-1</sup>x] + [cot<sup>-1</sup>x] = 0, where [.] denotes the greatest integer function, t...
If [cos-1x] + [cot-1x] = 0, where [.] denotes the greatest integer function, then complete set of values of x is
A
(cos 1,1]
B
(cos 1, cot 1)
C
(cot 1, 1]
D
[0, cot 1)
Answer
(cot 1, 1]
Explanation
Solution
We have [cos−1 x] ≥ 0 ∀ x ∈ [-1, 1]
and [cos-1x] ≥ 0 ∀ x ∈ R
⇒ [cos−1x] + [cot-1x] = 0
⇒ [cos-1x] = [cot-1x] = 0 If [cos-1x] = 0
⇒ x ∈ (cos 1, 1]
If [cot-1x] = 0
⇒ x ∈ (cot-1x, ∞)
⇒ x ∈ (cot 1, 1]