MCQ
If the two lines with slope $m_1$ and $m_2$ are perpendicular then their slopes has relation:
  • A
    $m_1+m_2=1$
  • B
    $m_1 \times m_2=1$
  • $m_1 \times m_2=-1$
  • D
    $m_1+m_2=-1$

Answer

Correct option: C.
$m_1 \times m_2=-1$
  1. $m_1 \times m_2=-1$
Solution:
If the two lines are perpendicular then if one line form angle $\alpha$ with positive x-axis then the other line form angle $90^\circ + \alpha$
If $\text{m}_{1} = \tan \alpha$ then $m_2$ will be $\tan (90^\circ + \alpha) = -\cot\alpha = \frac{-1}{\tan\alpha}$
$\Rightarrow m_1 \times m_2 = -1$.

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