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JEE Main202125 Feb 2021Morning ShiftMathematicsTrigonometric EquationsActual

All possible values of θ ∈ 0 , 2 π for which sin 2 θ + tan 2 θ > 0 lie in :

Options

  1. A0 , π 2 ∪ π , 3 π 2
  2. B0 , π 2 ∪ π 2 , 3 π 4 ∪ π , 7 π 6
  3. C0 , π 4 ∪ π 2 , 3 π 4 ∪ π , 5 π 4 ∪ 3 π 2 , 7 π 4
  4. D0 , π 4 ∪ π 2 , 3 π 4 ∪ 3 π 2 , 11 π 6

Correct answer

C. 0 , π 4 ∪ π 2 , 3 π 4 ∪ π , 5 π 4 ∪ 3 π 2 , 7 π 4

Step-by-step solution

sin 2 θ + tan 2 θ > 0 ⇒ sin 2 θ + sin 2 θ cos 2 θ > 0 ⇒ sin 2 θ cos 2 θ + 1 cos 2 θ > 0 ⇒ tan 2 θ 2 cos 2 θ > 0 Note: cos 2 θ ≠ 0 ⇒ 1 - 2 sin 2 θ ≠ 0 ⇒ sin θ ≠ ± 1 2 Now, tan 2 θ 1 + cos 2 θ > 0 ⇒ tan 2 θ > 0 (as cos 2 θ + 1 > 0 ) ⇒ 2 θ ∈ 0 , π 2 ∪ π , 3 π 2 ∪ 2 π , 5 π 2 ∪ 3 π , 7

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