Easy MCQ +4 / -1 PYQ · JEE Mains 2021

If $\alpha$, $\beta$ $\in$ R are such that 1 $-$ 2i (here i2 = $-$1) is a root of z2 + $\alpha$z + $\beta$ = 0, then ($\alpha$ $-$ $\beta$) is equal to :

  1. A $-$7 Correct answer
  2. B 7
  3. C 3
  4. D $-$3

Solution

1 $-$ 2i is the root of the equation. So other root is 1 $+$ 2i <br><br>$\therefore$ Sum of roots = 1 $-$ 2i + 1 $+$ 2i = 2 = -$\alpha$ <br><br>Product of roots = (1 $-$ 2i)(1 $+$ 2i) = 1 - 4i<sup>2</sup> = 5 = $\beta$ <br><br>$\therefore$ $\alpha$ - $\beta$ = -2 - 5 = -7

About this question

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

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