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What is a pencil, a compass. and a straightedge in GeoGebra?

Here is a little mathcast (video) explaining the tools we will use ...

Read about it   (printable pdf)

Try the tools online or download: BasicConstruct.ggb.

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What do we do when it says: Given ...?

Here is a little mathcast (video) explaining how to get the "givens" ...

Read about it   (printable pdf)

1. Given a point A ...

2. Given a line m and a point A on m ...

3. Given a line m ...

4. Given an angle α ...

5. Given a circle c ...

How do we do and undo? (a few more techniques)

Here is a little mathcast (video) explaining a few more useful techniques ...

Read about it   (printable pdf)

1. Using the Intersection Point Tool   

2. Using the Compass Tool    - the tool that does:

"I need a circle with center A and with a radius the distance between B and C."

"a.k.a. Take your compass and stick the needle in point B and widen it until it reaches point C.
 Now stick the needle in point A and draw a circle."

3. Undo/Redo /   
4. Forget the order in which you constructed? Look at the Construction Protocol.  
5. Making nice and readable constructs (decorating your objects)

Seven basic compass and straightedge constructions UPDATED: May 2009

1. Copy a line segment.  Complete interactivity

Given: A line segment with start point A and a line with point P on it.
Goal:   Construct a on this line with start point P.

           (Congruent: the lengths of the segments are equal).

2. Copy a triangle (side-side-side).  in progress

Given: A triangle ΔABC and a line with a point P on it.
Goal: Construct a congruent triangle ΔPRS such that the line segment \overline{PR} lies on the given line.
coming soon

3. Copy an angle.  Complete interactivity

Given: An angle α with vertex A.
Goal: Copy angle α onto a line with point P so that P is the vertex.

           (Congruent: the sizes of the angles are equal).

4. bisect a line segment  (in progress)

Given: A line segment \overline {AB} .
Goal: Construct the point C \overline {AB} that is halfway between A and B.

5. Construct a perpendicular (normal).  Mathcast updated:30 August 2008

Given: a line m \,\,with a point A \,\,on m \,\,.
Goal: Construct a line n passing through A \,\,and perpendicular (normal) to m \,\,.

6. Bisect an angle

Given: An angle.
Goal: Construct the ray that bisects this angle (divides it into two equal angles).

7. Construct a parallel -(uses idea of transversal)

Given: A line m \,\,and a point C \,\, NOT on m \,\,.
Goal: Construct (find) a line p passing through C \,\,and parallel to m \,\,.

Related themes:


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geometric, construct, construction, straightedge, compass, ruler, geogebra, application, geometry, program

Page last modified on May 25, 2009, at 08:28 AM