MCQ
If the difference between the roots of the equation $x^2 + ax + b = 0$ is equal to the difference between the roots of the equation $x^2 + bx + a = 0 (a \ne  b)$ , then 
  • A
    $a + b = 4$
  • $a + b =  -4$
  • C
    $a -b = 4$
  • D
    $a -b =  -4$

Answer

Correct option: B.
$a + b =  -4$
b
$\alpha-\beta=\alpha^{\prime}-\beta^{\prime}$

$(\alpha+\beta)^{2}-4 \alpha \beta=\left(\alpha^{\prime}+\beta^{\prime}\right)^{2}-4 \alpha^{\prime} \beta^{\prime}$

$\Rightarrow a^{2}-4 b=b^{2}-4 a$

${a^{2}-b^{2}=4(b-a)} $

${(a-b)(a+b)=-4(a-b)}$

$\Rightarrow(a+b)=-4$

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