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Math Help - Construct an angle

  1. #1
    Senior Member Mukilab's Avatar
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    Construct an angle

    A question tells me to construct an angle using a ruler and a pair of compasses.

    No idea how to do this without a protractor, any help?
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  2. #2
    Super Member Deadstar's Avatar
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    Quote Originally Posted by Mukilab View Post
    A question tells me to construct an angle using a ruler and a pair of compasses.

    No idea how to do this without a protractor, any help?
    Compass and straightedge constructions - Wikipedia, the free encyclopedia
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  3. #3
    Senior Member Mukilab's Avatar
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    Doesn't tell me how to create an angle using only a ruler and compass
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  4. #4
    Senior Member Mukilab's Avatar
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    Any other help?

    I've thought about this and I don't know how it can be feasibly possible without extensive working and no calculator.

    Surely there must be some error because you can simply do this with a protractor and ruler.
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  5. #5
    Super Member Deadstar's Avatar
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    Quote Originally Posted by Mukilab View Post
    Any other help?

    I've thought about this and I don't know how it can be feasibly possible without extensive working and no calculator.

    Surely there must be some error because you can simply do this with a protractor and ruler.
    Isn't it amazing that the link shows a few being constructed then...

    Which angle are you trying to do.
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  6. #6
    Senior Member Mukilab's Avatar
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    I have a single line. From that single line I am supposed to construct an angle of 30 degrees.
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  7. #7
    Super Member Deadstar's Avatar
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    How to construct (draw) a 30 degree angle with compass and straightedge or ruler - Math Open Reference

    Or construct a equilateral triangle using the wiki link and figure out how to divide an angle in two...

    These take a bit of time to explain so google is the best bet.
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  8. #8
    Senior Member Mukilab's Avatar
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    thanks, there are so many new things on that site. I wonder how these can be proved without measurement.
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  9. #9
    Newbie hungthinh92's Avatar
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    Actually, if you want to find 30 degree angle with compass and ruler, you can do like this:
    A. Draw an equilateral triangle:
    Step 1: Draw a random line.
    Step 2: Put the point of your compass at one end of the segment and the pencil point at the other.
    Step 3: Without moving the point of the compass and without changing how wide it is set, swing the compass in approximately a quarter-circle (up & away from the line segment).
    Step 4: Without changing how wide the compass is spread, move the compass point to the other end.
    Step 5: Swing the compass so that the arc you are creating crosses the arc you drew in step 3.
    Step 6: Mark the place where the two arcs cross.
    Step 7: Using a ruler, draw line segments that connect the spot where the arcs cross to each end of the original line segment.
    B. Draw a height of the triangle.
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