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JEE Advanced 2015Paper 2
Exam
JEE Advanced
Year
2015
Paper
Paper 2
Subject
Mathematics
Chapter
Quadratic Equation

JEE Advanced 2015 · Paper 2 · Mathematics · Quadratic Equation

Let S be the set of all non - zero real numbers α such that the...

Let S be the set of all non - zero real numbers α\alpha such that the quadratic equation αx2−x+α=0\alpha{x}^{2} - x + \alpha = 0 has two distinct real roots x1andx2{x}_{1}and{x}_{2} satisfying the inequality \left|{x}_{1} - {x}_{2}\right| < 1 .$ Which of the following intervals is(are) a subset(s) of S?

Options

  1. A(−12,−15)\left(- \dfrac{1}{2}, - \dfrac{1}{\sqrt{5}}\right)
  2. B(−15,0)\left(- \dfrac{1}{\sqrt{5}}, 0\right)
  3. C(0,15)\left(0, \dfrac{1}{\sqrt{5}}\right)
  4. D(15,12)\left(\dfrac{1}{\sqrt{5}}, \dfrac{1}{2}\right)

Correct answer

A. (−12,−15)\left(- \dfrac{1}{2}, - \dfrac{1}{\sqrt{5}}\right)

Step-by-step solution

\alpha{x}^{2} - x + \alpha = 0<br>∣x1−x2∣<0<br > \left|{x}_{1} - {x}_{2}\right| < 0
\left|\dfrac{\sqrt{1 - 4{\alpha}^{2}}}{\alpha}\right| < 1<br><br >\sqrt{1 - 4{\alpha}^{2}} < | \alpha |<br><br >1 - 4{\alpha}^{2} < {\alpha}^{2}<br><br >{\alpha}^{2} - \dfrac{1}{5} > 0<br><br >\alpha \in \left(- \infty, - \dfrac{1}{\sqrt{5}}\right) \cup \left(\dfrac{1}{\sqrt{5}}, \infty\right)<br>Also,<br >Also,1 - 4{\alpha}^{2} > 0<br><br >{\alpha}^{2} - \dfrac{1}{4} < 0<br>(α−12)(α+12)<0<br > \left(\alpha - \dfrac{1}{2}\right)\left(\alpha + \dfrac{1}{2}\right) < 0
α∈(−12,12)\alpha \in \left(- \dfrac{1}{2}, \dfrac{1}{2}\right)
Taking intersection
α∈(−12,−15)∪(15,12)\alpha \in \left(- \dfrac{1}{2}, - \dfrac{1}{\sqrt{5}}\right) \cup \left(\dfrac{1}{\sqrt{5}}, \dfrac{1}{2}\right)
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