Statement I: lf mcos(θ+α)=ncos(θ−α), then tanθtanα=m+nm−n. Statement II: If sin(α+β)sin(α−β)=a+ba−b, then tanα.cotβ=ab. Which of the above statements is correct?
A
Only I
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B
Only II
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C
Both I & II
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D
Neither l nor ll
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Solution
The correct option is B Only II Hence cos(θ+α)cos(θ−α)=nm Hence cos(θ+α)+cos(θ−α)cos(θ+α)−cos(θ−α)=n+mn−m 2cosθ.cosαcosθ.cosα−sinθ.sinα−(cosθ.cosα+sinθ.sinα)=n+mn−m 2cosθ.cosα−2sinθ.sinα=−n+mm−n Hence cotθ.cotα=m+nm−n sin(β+α)sin(β−α)=b+ab−a Hence sin(β+α)+sin(β−α)sin(β+α)−sin(β−α)=ab 2cosβ.sinα2sinβ.cosα=ab cotβ.tanα=ab