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Rajan@2021
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Using the formula, cos A = √(1+cos 2A)/ 2 , find the value of cos 30° , it being given that cos 60° = 1/2 .

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This is the basic and conceptual question from trigonometric ratios in which we have cos A = √(1+cos 2A)/ 2, it being given that cos 60° = 1/2

And we have to find the value of cos 30°

RS Aggarwal, Class 10, chapter 11, question no 18

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1 Answer

  1. Put A=30 then 2A=60cosA = √(1+cos2A)/2

    cos30= √(1+cos60∘)/2
                ​=√(1+1/2)/2
                ​=√3/2/2
    The value of cos30 is √3/2

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