Q23 / 83 · NTA Abhyas (JEE Main) 2020 · Mathematics · Trigonometric Equations

In the interval -π2,π2, the equation logsin⁡θ⁡cos⁡2θ=2 has

  • A
    no solution
  • Correct answer
    B
    a unique solution
  • C
    two solutions
  • D
    infinite many solutions

Solution

Since, -π2≤θ≤π2⇒sin⁡θ∈-1,1
Here sin⁡θ∈0,1 for logsin⁡θ⁡cos⁡2θ=2 to be defined.
⇒cos⁡2θ=sin2⁡θ
⇒1-2sin2⁡θ=sin2⁡θ
⇒sin2⁡θ=13⇒sin⁡θ=13 (as sin⁡θ∈0,1 )
⇒The equation has a unique solution.

Hence, the correct answer is option: 'B'.

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