Question

    Given that 'θ' is an angle less than 120 °

    , what is the value of 'θ' if it satisfies the equation 3cos 2 θ = 2 + sin 2 θ.
    A 90° Correct Answer Incorrect Answer
    B 60° Correct Answer Incorrect Answer
    C 30° Correct Answer Incorrect Answer
    D 45° Correct Answer Incorrect Answer

    Solution

    Given, 3cos 2 θ = 2 + sin 2 θ

    3cos 2 θ - sin 2  θ = 2

    3cos 2 θ - (1 - cos 2  θ) = 2

    4cos 2 θ = 3

    cos 2 θ = (3/4)

    cosθ = √3/2 (Since, in options maximum value of 'θ' is 90 o  therefore, we will take the positive root only)

    cosθ = cos30 o

    θ = 30 o

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