Maths · Inverse trigonometrical functions and their properties

Solve: \) is real if

Solve: \( \operatorname{cosec}^{-1}(\cos x) \) is real \( , \) if

  • A. \( x \in[-1,1] \)
  • B. \( x \in R \)
  • C. \( x \) is an odd multiple of \( \frac{\pi}{2} \)
  • D. x is a multiple of \( \pi \)

Step-by-step solution

cosec^{-1}(y) is real only if |y| ≥ 1. Here y = cos x, and |cos x| ≤ 1. Equality holds only when |cos x| = 1, i.e., cos x = ±1. This occurs when x = nπ, n ∈ Z. Thus x must be a multiple of π.
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