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Thread: two lines and a circle construction

  1. #1

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    Wink two lines and a circle construction

    Here is something that I came across while solving another problem. I do not know the answer to this question - yet
    With only a compass and straight edge, Given two intersecting lines and a circle, construct a circle that is tangent to the three objects. If anyone could save me some time figuring this out I would be grateful.
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  2. #2
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    I do not know how to solve your problem, but you should start by drawing the bisector of the angle between the two intersecting lines.

    A circle tangent to both lines will be on that bisector.

    Next, I would experimentally draw a good approximation to a solution. A little fooling around should get you a good diagram.

    Analyzing the diagram might give you a clue.
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  3. #3
    transcendental analytic kedaman's Avatar
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    (X1-x1)^2+(Y1-y1)^2=r1^2
    (X1-x2)^2+(Y1-y2)^2=r2^2
    Y2-y3=k3(X2-x3)
    (X2-x1)^2+(Y2-y1)^2=r1^2
    Y3-y4=k4(X3-x4)
    (X3-x1)^2+(Y3-y1)^2=r1^2
    solve r1, x1 and y1. r2,x2,y2 is your arbitrary chosen circle, k3,x3,y3 and k4,x4,y4 your lines, k3!=k4.
    further on you have the intersections X1,Y1 between the circles, X2,Y2 and X3,Y3 between the drawn circle and each line.
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  4. #4
    transcendental analytic kedaman's Avatar
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    hmm you need to have
    (x1-x2)^2+(y1-xy)^2=(r1+r2)^2
    k3=(x3-x1)/(y3-y1)
    k4=(x4-x1)/(y4-y1)
    as well
    Use
    writing software in C++ is like driving rivets into steel beam with a toothpick.
    writing haskell makes your life easier:
    reverse (p (6*9)) where p x|x==0=""|True=chr (48+z): p y where (y,z)=divMod x 13
    To throw away OOP for low level languages is myopia, to keep OOP is hyperopia. To throw away OOP for a high level language is insight.

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