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Published byJob Farmer Modified over 8 years ago
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Find the equation of a conic passing through five point (using the Organic construction)
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Example: Given five points: L1={(-4, -1), (-2, 3), (0, 2), (1, -5), (3, -2)}
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Sort and Shift these points so that one will be on the origin: L2={(0, 0), (2, 4), (4, 3), (5, -4), 97, -1)}
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Rotate all the points so that the last point will be on the x-axis: For example, if we want to move (7,-1) to the x-axis we must first must find the appropriate angle of rotation.
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We use the following matrix to rotate the points such that one point will be moved to the x-axis.
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Let us use this matrix to rotate (7,-1) to a point on the x-axis.
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If we continue in the similar manner, we can find the rotation of all the points. Let the point be called
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Let us find the parameters for the five point conic function. Points: A, B, C, D, and E. Angles: =<CAB and =<CBA
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Directrix: We rotate line AE about A to create line AE’ and line BE about B to create AB’. Call the intersection of both of these line E’. In a similar manner create point D’. Line D’E’ will be our directrix for the organic construction.
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Thus the directrix is the line passing through D’ and E’; (1)
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Now, using =<BAC and =<ABC for our angles of rotation with the points of the directrix to get the following equation. ( 2 )
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Graph of curve
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The using the matrix of rotation we will rotate back the conic and the directrix.
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Plug in x and y into (1), (2) and simplify the expression. (3) (4)
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Translate the conic and directrix to the original position by using the following equalities.
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Plug in x’ and y’ into (3), (4) and simplify the expression. (5) (6)
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