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Heres my scenario.. I have two parallel lines segments,AB and CD of equal length. If A,B are known, how do I find C and D?!

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closed as off-topic by Davide Giraudo, Grigory M, Shuchang, Daniel Rust, Dennis Gulko Dec 23 '13 at 12:26

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2 Answers 2

You cannot, since there are infinitely many lines parallel to AB.

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sorry! my bad.. the perpendicular distance between the lines is known.. should have mentioned that in the question.. –  SatheeshJM Jan 23 '13 at 9:48
    
you want ABCD be a rectangle? On which side of AB you want CD to stay? –  Emanuele Paolini Jan 23 '13 at 10:12

$x_3,y_3$ can be arbitrary. Then let $x_4=x_3+x_2-x_1, y_4=y_3+y_2-y_1$.

If you more specifically want $ABDC$ to be a rectangle, select $t$ arbitrary, then let $x_3=x_1+t(y_2-y_1), y_3=y_1+t(x_1-x_2)$ in the above.

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