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JEE Advanced 2016 · Complex Numbers and Quadratic Equations

Let −π6<θ<−π12-\frac{\pi}{6}<\theta<-\frac{\pi}{12}. Suppose θ1\theta_{1} and B1B_{1} are the roots of the equation x2−2xsec⁡θ+1=0x^{2}-2x\sec\theta+1=0 and α2\alpha_{2} and β2\beta_{2} are the roots of the equation x2+2xtan⁡θ−1=0x^{2}+2x\tan\theta-1=0. If α1>β1\alpha_{1}>\beta_{1} and α2>β2\alpha_{2}>\beta_{2}, then α1+β2\alpha_{1}+\beta_{2} equals

Answer: C. −2tan⁡θ-2\tan\theta

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Let -π/6<θ<-π/12. Suppose θ₁ and B₁ are the roots of the equation x²-2xsecθ+1=0 and α₂ and β₂ are the roots of the equation x²+2xtanθ-1=0. If α₁>β₁ and α₂>β₂, then α₁+β₂ equals −π6<θ<−π12-\dfrac{\pi}{6} < \theta < -\dfrac{\pi}{12} i.e. θ∈(−30∘,−15∘)\text{i.e. } \theta \in (-30^\circ, -15^\circ) x2−2xsec⁡θ+1=0→α1, β1x^{2}-2x\sec\theta+1=0 \to \alpha_{1},\ \beta_{1} x2+2xtan⁡θ−1=0→α2, β2x^{2}+2x\tan\theta-1=0 \to \alpha_{2},\ \beta_{2} Find α1+β2\text{Find } \alpha_{1}+\beta_{2} x=−b±b2−4ac2ax = \dfrac{-b \pm \sqrt{b^{2}-4ac}}{2a} tan⁡θ<0,sec⁡θ>0 for this θ\tan\theta < 0,\quad \sec\theta > 0 \text{ for this } \theta x=2sec⁡θ±4sec⁡2θ−42x = \dfrac{2\sec\theta \pm \sqrt{4\sec^{2}\theta-4}}{2} =sec⁡θ±sec⁡2θ−1= \sec\theta \pm \sqrt{\sec^{2}\theta-1} sec⁡2θ−1=tan⁡2θ\sec^{2}\theta-1 = \tan^{2}\theta x=sec⁡θ±∣tan⁡θ∣x = \sec\theta \pm |\tan\theta| ∣tan⁡θ∣=−tan⁡θ|\tan\theta| = -\tan\theta x=sec⁡θ−tan⁡θ  or  sec⁡θ+tan⁡θx = \sec\theta - \tan\theta \ \text{ or } \ \sec\theta + \tan\theta α1=sec⁡θ−tan⁡θ,β1=sec⁡θ+tan⁡θ\alpha_{1} = \sec\theta - \tan\theta,\quad \beta_{1} = \sec\theta + \tan\theta α1+β1=2sec⁡θ,α1β1=sec⁡2θ−tan⁡2θ=1\alpha_{1}+\beta_{1} = 2\sec\theta,\quad \alpha_{1}\beta_{1} = \sec^{2}\theta-\tan^{2}\theta = 1 x=−2tan⁡θ±4tan⁡2θ+42x = \dfrac{-2\tan\theta \pm \sqrt{4\tan^{2}\theta+4}}{2} =−tan⁡θ±tan⁡2θ+1= -\tan\theta \pm \sqrt{\tan^{2}\theta+1} tan⁡2θ+1=sec⁡2θ\tan^{2}\theta+1 = \sec^{2}\theta x=−tan⁡θ±∣sec⁡θ∣x = -\tan\theta \pm |\sec\theta| ∣sec⁡θ∣=sec⁡θ|\sec\theta| = \sec\theta x=sec⁡θ−tan⁡θ  or  −tan⁡θ−sec⁡θx = \sec\theta - \tan\theta \ \text{ or } \ -\tan\theta - \sec\theta α2=sec⁡θ−tan⁡θ,β2=−tan⁡θ−sec⁡θ\alpha_{2} = \sec\theta - \tan\theta,\quad \beta_{2} = -\tan\theta - \sec\theta α2+β2=−2tan⁡θ,α2β2=−1\alpha_{2}+\beta_{2} = -2\tan\theta,\quad \alpha_{2}\beta_{2} = -1 α1+β2=(sec⁡θ−tan⁡θ)+(−tan⁡θ−sec⁡θ)\alpha_{1}+\beta_{2} = (\sec\theta-\tan\theta)+(-\tan\theta-\sec\theta) =−2tan⁡θ= -2\tan\theta α1+β2=−2tan⁡θ ⇒ option (3)\alpha_{1}+\beta_{2} = -2\tan\theta \ \Rightarrow\ \text{option (3)}

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