NextMockSearch exams, e.g. SSC CGL, UPPSC, Lekhpal
Railways PYQCBT 1 2020

RRB NTPC · Question 45

If cos 2θ = sin θ and θ lies between 0 and 90°, then θ will be:

  1. 60°

  2. 30°

  3. 45°

  4. None of these

Show answer & explanation

Answer: (B) 30°

Explanation

cos 2θ = 1 − 2sin²θ = sin θ, so 2sin²θ + sin θ − 1 = 0 and sin θ = 1/2. With θ between 0° and 90°, θ = 30°.