Question 220241
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It depends on what information you have about the lines.  Not knowing your starting point, all I can say is the following:

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

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