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Browse High School Euclidean/Plane Geometry
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Classifying quadrilaterals.
Pythagorean theorem proofs.
 Building a Geometric Proof [06/03/1999]

Can you explain how to do a twocolumn proof?
 Explementary Angles [05/29/2003]

What do we call two angles that add up to 360 degrees?
 Geometry Proofs [11/07/2001]

General and specific advice for a student having trouble writing proofs
on her own.
 Is a Sphere 2D or 3D? [8/8/1996]

Is a sphere a two or a threedimensional object?
 Measuring Angles with a Protractor [02/28/2002]

I want to know how to measure acute, reflex and obtuse angles with a
protractor.
 Painting Cubes [01/06/2003]

How many unit cubes would be needed to create a cube with a side
length of 3 units? If you painted the larger cube and broke it up
into unit cubes, how many faces of each unit cube would be painted?
 Remembering Area Formulas [12/23/2001]

Is there was a good way to help me memorize the formulas for areas of
different shapes?
 About Basic Geometry [10/14/1998]

Who developed basic geometry? What is it used for? Who uses it?
 Abraham Kaestner and Euclid's Fifth (Parallel) Postulate [12/02/1996]

Where can I find information on Abraham Kaestner?
 Aframe for Swing [07/26/1997]

I am trying to build a stand for a swing. The ends are Aframes out of 4
by 4's... what is the angle of the miter cut?
 The Algebra of Complements and Supplements [01/25/1999]

What are complements and supplements? How do you translate these concepts
into algebra?
 Alternate and Corresponding Angles [10/21/1996]

Please explain corresponding and alternate angles.
 Alternate Exterior Angles [06/03/2002]

What is an 'alternate exterior angle'?
 Analytical Geometry [04/11/2002]

When two straight lines meet each other perpendicularly, the product
of their slopes is 1. However, x and y axes meet at 90 degrees, but
the product of their slopes is not 1. Why?
 Angle Inscribed in a Semicircle [11/07/2001]

Prove that any angle inscribed in a semicircle is a right angle.
 Angles as Turns [05/29/2003]

How can angles be negative?
 Angles Greater than 360 Degrees [01/01/1999]

We know the definitions of acute, obtuse, and reflex angles, but we were
debating what kind of angle a 425 degree angle is.
 Angle, Side Length of a Triangle [9/4/1996]

What is the relation between the angles and side lengths of a triangle?
 The Angles of a Roof [11/20/1995]

I am trying to build a model house but am having trouble with laying out
the roof. The main part of the house has a peaked roof (an "A" frame
house); the angle formed when the roof meets the ground is 60 degrees.
There is an addition onto the Aframe with a 30 degree angle formed to
the walls. What angle should the addition's roof be cut at so it meets
the Aframe roof?
 Angles of Stars [08/18/1997]

What are the interior and external angles of stars built on regular
pentagons and octagons.
 Angle Trisection: Construction vs. Drawing [10/17/2001]

Has anyone ever divided an angle into three equal parts by construction?
I have been told it has not been accomplished.
 Another Grazing Cow [6/7/1995]

A man has a barn that is 20 ft by 10 ft. He tethers a cow to one corner
of the outside of the barn using a 50ft rope. What is the total area
that the cow is capable of grazing?
 Ant and Rectangle [01/22/2001]

Does the ant walk along the diagonals of the rectangle?
 Area and Perimeter: Isoperimetric Quotient [12/05/2001]

What is the isoperimetric quotient of a twodimensional shape? Is it a
measure of compression?
 Area and Perimeter: Mowing the Lawn [6/1/1996]

How many circuits are necessary to cut half the lawn?
 Area, Circumference of an Ellipse [7/29/1996]

How do I calculate the area and circumference of a given ellipse?
 Are All Triangles Isosceles? [09/15/1999]

Can you help me find the flaw in this 'proof' claiming that all triangles
are isosceles?
 Are Angles Dimensionless? [08/31/2003]

If you look at the dimensions in the equation arc length = r*theta, it
appears that angles must be dimensionless. But this can't be right.
Or can it?
 Area of a Circle with Radius less than 1 [02/18/2002]

If the radius is less than 1 it just gets smaller and you get a smaller
area...
 Area of an Ellipse Cut by a Chord [05/26/2000]

How can you calculate area of the part of an ellipse cut off by a chord,
if you know the major and minor axes, and the chord?
 Area of an Inscribed Quadrilateral [05/11/2000]

Given a quadrilateral where the midpoints of each side are connected to
form a new quadrilaterals inside the first, what is the ratio of the area
of the larger quadrilateral to the smaller one?
 Area of a Rectangle Outside a Rectangle [6/11/1996]

Find the area of the concrete border of a rectangular swimming pool.
 Area of a Reuleaux Triangle [06/13/2002]

Could you please help me find a formula to find the area of a
Reuleaux triangle?
 Area of Intersection of Two Circular Segments [04/20/2007]

Given a circle of radius r and center c, suppose two intersecting
chords AB and CD (intersecting in P) form two circular segments. How
do I compute the area of the intersection of the two circular segments?
 Areas of House Lots [02/18/1998]

We have to determine sanitary sewer assessments of properties based on
the square feet of their lots. Many lots are 4sided but do not have any
parallel lines...
 Arrange 7 Points in a Plane... [10/05/1998]

Arrange 7 points in a plane so that if any three are chosen, at least 2
of them will be a unit distance apart.
 Azimuth Angle [09/08/1998]

Can you give me the formula for the azimuth angle and explain some of the
terminology?
 Ball Bouncing off a Line Segment [05/04/2001]

If you take an arbitrary line on a 2D plane, e.g. x1y1  x2y2, then take
a point that moves about the plane, say pxpy, can you tell if this point
has crossed the line at any time?
 Barycentric Calculus [01/06/1999]

How does barycentric calculus compare with trilinear or cartesian
calculus?
 Betweenness of Points on a Line Idea and Proof [06/26/2008]

Could someone explain betweenness of points on a line and why it's important? I also don't understand the way my book proves it.
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