MCQ
The equation $2{\cos ^{ - 1}}x + {\sin ^{ - 1}}x = \frac{{11\pi }}{6}$ has
  • No solution
  • B
    Only one solution
  • C
    Two solutions
  • D
    Three solutions

Answer

Correct option: A.
No solution
a
(a) Given equation is $2{\cos ^{ - 1}}x + {\sin ^{ - 1}}x = \frac{{11\pi }}{6}$

==> ${\cos ^{ - 1}}x + ({\cos ^{ - 1}}x + {\sin ^{ - 1}}x) = \frac{{11\pi }}{6}$

==> ${\cos ^{ - 1}}x + \frac{\pi }{2} = \frac{{11\pi }}{6}$

$ \Rightarrow {\cos ^{ - 1}}x = 4\pi /3$

which is not possible as ${\cos ^{ - 1}}x \in [0,\,\pi ]$.

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