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Find the condition for two straight lines to be perpendicular |
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Answer» let slope of lines l1 and l2 are respectively m1 and m2. we know that the the angle between two lines whose slopes are m1 & m2 is given by tanθ = \(\frac{m_1\,-\,m_2}{1\,+\,m_1\,m_2},\).....(1) where θ is angle between lines l1 and l2. for lines l1 & l2 to be perpendicular, we have θ = 90° \(\Rightarrow\) tanθ = tan90° = ∞ = \(\frac{1}{0}\) therefore, equation (i), we have \(\frac{m_1\,-\,m_2}{1\,+\,m_1\,m_2}=\frac{1}{0}\) \(\Rightarrow\) 1 + m1 m2 = 0 \(\Rightarrow\) m1 m2 = -1. Hence, two straight line are perpendiculer is the product of there slopes is equal to -1. |
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