Question 250322
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*[tex \LARGE \ \ \ \ \ \ \ \ \ \  L_1\ \parallel\ L_2 \ \ \Leftrightarrow\ \ m_1\ =\ m_2]


If the lines are parallel, the slopes are equal



*[tex \LARGE \ \ \ \ \ \ \ \ \ \  L_1\ \perp\ L_2 \ \ \Leftrightarrow\ \ m_1\ =\ -\frac{1}{m_2}\text{ and } m_1,\, m_2\, \neq\, 0]


If the lines are perpendicular, then the slopes are negative reciprocals.  (invert the fraction and put a minus sign in front of it - or take the minus sign away if there was already one there)



John
*[tex \LARGE e^{i\pi} + 1 = 0]
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