# Basic Geometric Constructs: Compass and Straightedge with GeoGebra

*** To use this offline today, you need to get the pre-release of GeoGebra 3.1:  Click here ***

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

Here is a little mathcast (video) explaining the tools we will use ...   Try the tools online or download: BasicConstruct.ggb.

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

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

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 ...

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