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NDA 2018
Exam
NDA
Year
2018
Subject
Mathematics
Chapter
Quadratic Equation

NDA 2018 · Mathematics · Quadratic Equation

The equation |1-x|+x^2=5 has

The equation ∣1−x∣+x2=5|1-x|+x^2=5 has

Options

  1. Aa rational root and an irrational root
  2. Btwo rational roots
  3. Ctwo irrational roots
  4. Dno real roots

Correct answer

A. a rational root and an irrational root

Step-by-step solution

∣1−x∣+x2=5⇒∣x−1∣+x2=5\begin{aligned} & |1-x|+x^2=5 \\ & \Rightarrow|x-1|+x^2=5 \end{aligned} First case: If x<1,∣x−1∣x < 1,|x-1| is negative. ∴−(x−1)+x2=5⇒−x+1+x2=5⇒x2−x+1=5⇒x2−x−4=0 Roots are −(−1)±(−1)2−4(1)(−4)2(1)\begin{aligned} & \therefore \quad-(\mathrm{x}-1)+\mathrm{x}^2=5 \\ & \Rightarrow-\mathrm{x}+1+\mathrm{x}^2=5 \\ & \Rightarrow \mathrm{x}^2-\mathrm{x}+1=5 \\ & \Rightarrow \mathrm{x}^2-\mathrm{x}-4=0 \\ & \text{ Roots are } \frac{-(-1) \pm \sqrt{(-1)^2-4(1)(-4)}}{2(1)} \end{aligned}=\frac{1 \pm \sqrt{1+16}}{2}=\frac{1 \pm \sqrt{17}}{2}Since,Since,x < 1,rootcannotbe, root cannot be\frac{1+\sqrt{17}}{2}.So,therootis. So, the root is\frac{1-\sqrt{17}}{2},whichisirrational.Secondcase:If, which is irrational. Second case: Ifx > 1,|x-1|=x-1∴∣x−1∣+x2=5⇒x−1+x2=5⇒x2+x−6=0⇒x2+3x−2x−6=0⇒x(x+3)−2(x+3)=0⇒x=2,−3\begin{array}{ll} \therefore & |\mathrm{x}-1|+\mathrm{x}^2=5 \\ \Rightarrow & \mathrm{x}-1+\mathrm{x}^2=5 \\ \Rightarrow & \mathrm{x}^2+\mathrm{x}-6=0 \\ \Rightarrow & \mathrm{x}^2+3 \mathrm{x}-2 \mathrm{x}-6=0 \\ \Rightarrow & \mathrm{x}(\mathrm{x}+3)-2(\mathrm{x}+3)=0 \\ \Rightarrow & \mathrm{x}=2,-3 \end{array} Since x>1x > 1, root cannot be -3 . So, root is 2 which is rational. ∴\therefore \quad given expression has one irrational root and one rational root.$
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