Maths · Inverse trigonometrical functions and their properties

If +\cot ^{-1}\left(\frac{1}{x-1}\right)= \) then

If \( \cot ^{-1}\left(\frac{1}{x+1}\right)+\cot ^{-1}\left(\frac{1}{x-1}\right)= \) \( \tan ^{-1} 3 x-\tan ^{-1} x \) then \( \boldsymbol{x}= \)

  • A. \( \pm 1 / 2 \)
  • B. \( -1, \pm 1 / 3 \)
  • C. 2,±1
  • D. \( -1 . \pm 1 / 2 \)

Step-by-step solution

Transform cot^{-1}(1/(x+1)) and cot^{-1}(1/(x-1)) into tan^{-1}(x+1) and tan^{-1}(x-1) using the identity cot^{-1}(1/a)=tan^{-1}(a) for a>0, with appropriate adjustments for sign. Simplify the equation using the formula for tan^{-1}(u) - tan^{-1}(v). Taking tangent on both sides yields 2x/(2-x^2)=2x/(1+3x^2). Solving gives x=0 or x=±1/2. x=0 does not satisfy the original equation, so x=±1/2 are the solutions, though domain conditions must be considered.
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