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JEE Main 2024
Trigonometry
Trigonometric Ratio and Identites
Hard

Question

For α,β(0,π/2)\alpha, \beta \in(0, \pi / 2), let 3sin(α+β)=2sin(αβ)3 \sin (\alpha+\beta)=2 \sin (\alpha-\beta) and a real number kk be such that tanα=ktanβ\tan \alpha=k \tan \beta. Then, the value of kk is equal to

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Solution

To find the value of kk, the given conditions are: 3sin(α+β)=2sin(αβ)3 \sin (\alpha+\beta)=2 \sin (\alpha-\beta) And tanα=ktanβ\tan \alpha = k \tan \beta For the first equation, using the sum and difference formulas for sine, we can rewrite the equation as: 3(sinαcosβ+cosαsinβ)=2(sinαcosβcosαsinβ)3(\sin \alpha \cos \beta + \cos \alpha \sin \beta) = 2(\sin \alpha \cos \beta - \cos \alpha \sin \beta) Simplifying this, we get: 3sinαcosβ+3cosαsinβ=2sinαcosβ2cosαsinβ3 \sin \alpha \cos \beta + 3 \cos \alpha \sin \beta = 2 \sin \alpha \cos \beta - 2 \cos \alpha \sin \beta Rearranging the terms, we obtain: 5sinβcosα=sinαcosβ5 \sin \beta \cos \alpha = - \sin \alpha \cos \beta Dividing both sides by sinαcosβ\sin \alpha \cos \beta, we get: 5sinβcosαsinαcosβ=1\frac{5 \sin \beta \cos \alpha}{\sin \alpha \cos \beta} = -1 Which simplifies to: 5tanβ=tanα5 \tan \beta = - \tan \alpha So, taking the reciprocal, we have: tanα=5tanβ\tan \alpha = -5 \tan \beta Therefore, by comparing this equation with the given tanα=ktanβ\tan \alpha = k \tan \beta, we find that k=5k = -5. Thus, the value of kk is 5-5 .

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