Which one of the following is correct in respect of f(x)=\frac{1}{\sqrt{|x|-x}} and g(x)=\frac{1}{\sqrt{x-|x|}}?

  1. A. f(x) has some domain and g(x) has no domain
  2. B. f(x) has no domain and g(x) has some domain
  3. C. f(x) and g(x) have the same domain
  4. D. f(x) and g(x) do not have any domain

Correct Answer: A. f(x) has some domain and g(x) has no domain

Explanation

For f(x), we need |x| - x \gt 0 \implies |x| \gt x, which holds for x \lt 0. So f(x) has domain (-\infty, 0). For g(x), we need x - |x| \gt 0 \implies x \gt |x|, which is false for all real x. So g(x) has no real domain.

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