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Question 7 - NCERT Exemplar - MCQ - Chapter 8 Class 10 Introduction to Trignometry

Last updated at July 12, 2023 by

Given that sin θ = a/b, then cos θ is equal to

(A) b/√(b^2  - a^2 )   

(B) b/a  

(C) √(b^2  - a^2 )/b   

(D) a/√(b^2  - a^2 )

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Question 7 Given that sin θ = 𝑎/𝑏, then cos θ is equal to (A) 𝑏/√(𝑏^2 − 𝑎^2 ) (B) 𝑏/𝑎 (C) √(𝑏^2 − 𝑎^2 )/𝑏 (D) 𝑎/√(𝑏^2 − 𝑎^2 ) Now, cos2 θ = 1 − sin2 θ Putting sin θ = 𝑎/𝑏 cos2 θ = 1−(𝑎/𝑏)^2 cos2 θ = 1−𝑎^2/𝑏^2 cos2 θ = (𝒃^𝟐 − 𝒂^𝟐)/𝒃^𝟐 Taking square root cos θ = ± √((𝑏^2 − 𝑎^2)/𝑏^2 ) cos θ = ± √(𝑏^2 − 𝑎^2 )/𝑏 Since only positive values are given in options cos θ = √(𝒃^𝟐 − 𝒂^𝟐 )/𝒃 So, the correct answer is (C)

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