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| Angle between two lines |
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| Dividing throughout by x2, we get |
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| This being a quadratic in m has two roots m1 and m2. |
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| If m1 and m2 are the slopes of the lines, then q, the angle between the lines is given by |
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| Corollary |
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| i) The straight lines are coincident if h2 - ab = 0. |
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| ii) The straight lines are perpendicular if a + b = 0. |
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