Question bank/JEE Main/Mathematics

JEE MainMathematicsModerateTrigonometry

If α,β,γ,δ\alpha,\beta,\gamma,\delta are the solutions of the
equation 
tan⁡(θ+π4)=3tan3θ\tan\left( \theta + \frac{\pi}{4} \right) = 3tan3\theta
(where no two solutions among these have equal tangents), then value of

tanα+tanβ+tanγ+tanδtan\alpha + tan\beta + tan\gamma + tan\delta is

Show answer and solution
tan⁡(θ+π4)=3tan⁡θ,1+tan⁡θ1−tan⁡θ=3(3tan⁡θ−tan⁡3θ1−3tan⁡2θ)\tan\left( \theta + \frac{\pi}{4} \right) = 3\tan\theta,\frac{1 + \tan\theta}{1 - \tan\theta} = 3\left( \frac{3\tan\theta - \tan^{3}\theta}{1 - 3\tan^{2}\theta} \right)
Let

tanθ=t⇒1+t1−t=3(3t−t31−3t2)tan\theta = t \Rightarrow \frac{1 + t}{1 - t} = 3\left( \frac{3t - t^{3}}{1 - 3t^{2}} \right)
⇒\Rightarrow 3t^4 - 6t^2 + 8t -1= 0 so, t_1 + t_2 + t_3 + t_4 =
0

∴tanα+tanβ+tanγ+tanδ=0\therefore tan\alpha + tan\beta + tan\gamma + tan\delta = 0

Source: Grass-G / M-23 Mathematics Paper 31 Dec FST.docx

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