0 [email protected]Guru Asked: April 5, 20212021-04-05T20:45:21+05:30 2021-04-05T20:45:21+05:30In: CBSE Using the formula, sin A = √(1−cos 2A)/ 2 , find the value of sin 30°, it being given that cos 60° = 1/2 . 0 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. cbse class 10rs aggarwaltrigonometric ratios Share Facebook 1 Answer Voted Oldest Recent MathsMentor Guru 2021-04-06T08:50:08+05:30Added an answer on April 6, 2021 at 8:50 am 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. 0 Reply Share Share Share on Facebook Share on Twitter Share on LinkedIn Share on WhatsApp Leave an answerLeave an answerCancel reply Featured image Select file Browse Add a Video to describe the problem better. Video type Youtube Vimeo Dailymotion Facebook Choose from here the video type. Video ID Put Video ID here: https://www.youtube.com/watch?v=sdUUx5FdySs Ex: "sdUUx5FdySs". Click on image to update the captcha. Save my name, email, and website in this browser for the next time I comment. Related Questions Solve the following quadratic equation: √2x²+7x+5√2=0. Solve the following quadratic equation: x²+3√3x-30=0 Solve the following quadratic equation: x²-(√3-1)x+√3=0 Solve the following quadratic equation: x²-3√5x+10=0 Solve the following quadratic equation: √3x²-2√2x-2√3=0

## 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.