Easy MCQ +4 / -1 PYQ · JEE Mains 2020

Let f(x) be a quadratic polynomial such that
f(–1) + f(2) = 0. If one of the roots of f(x) = 0
is 3, then its other root lies in :

  1. A (–3, –1)
  2. B (1, 3)
  3. C (–1, 0) Correct answer
  4. D (0, 1)

Solution

Let the other root is $\alpha$. <br><br>$\therefore$ f(x) = a(x – 3) (x – $\alpha$) <br><br>f(2) = a($\alpha$– 2) <br><br>f(–1) = 4a(1 + $\alpha$) <br><br>Given f(–1) + f(2) = 0 <br><br>$\Rightarrow$a($\alpha$ – 2 + 4 + 4$\alpha$) = 0 <br><br>$\Rightarrow$ 5$\alpha$ = -2 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;As a $\ne$ 0 <br><br>$\Rightarrow$ $\alpha$ = $-\frac{2}{5}$ = - 0.4 <br><br>$\therefore$ $\alpha$ $\in$ (–1, 0)

About this question

Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane

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