This is the basic and exam oriented question from trigonometric ratios in which we have given sin A = √(1−cos 2A)/ 2,
We have to find the value of sin 30°, if cos 60° = 1/2 .
RS Aggarwal, class 10, chapter 11, question no 19.
Rajan@2021Guru
Using the formula, sin A = √(1−cos 2A)/ 2 , find the value of sin 30°, it being given that cos 60° = 1/2 .
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Put A=30∘ then 2A=60∘
sinA=√(1−cos2A)/2
Squaring both side, we get
sin^2 A = (1−cos2A)/2
And,
sin^2 30∘ = (1−cos60∘)/2
=(1−1/2)/2
=1/4
sin 30∘ = 1/2.