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
Rajan@2021Guru
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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Put A=30∘ then 2A=60∘cosA = √(1+cos2A)/2
cos30∘ = √(1+cos60∘)/2
=√(1+1/2)/2
=√3/2/2
The value of cos30∘ is √3/2