A polygon is a closed figure made by joining
line segments, where each line segment intersects exactly two others.
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A vertex is the point where two sides of
a polygon meet.
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| Triangle - A three-sided polygon.
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Equilateral Triangle - A triangle having
all three sides of equal length.
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Isosceles Triangle - A triangle having
two sides of equal length.
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Scalene Triangle - A triangle having three
sides of different lengths.
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Acute Triangle - An acute triangle is a
triangle with all three angles less than 90°.
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Obtuse Triangle - An obtuse triangle is
a triangle with one angle more than 90°.
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Right Triangle - A triangle having a right
angle. One of the angles of the triangle measures 90 degrees.
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Quadrilateral - A four-sided polygon.
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Rectangle - A four-sided polygon having
all right angles.
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Square - A four-sided polygon having equal-length
sides meeting at right angles.
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Parallelogram - A four-sided polygon with
two pairs of parallel sides.
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Rhombus - A four-sided polygon having all
four sides of equal length.
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Trapezoid - A four-sided polygon having
exactly one pair of parallel sides.
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Hexagon - A six-sided polygon.
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Pentagon - A five-sided polygon.
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Heptagon - A seven-sided polygon.
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Octagon - An eight-sided polygon.
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Nonagon - A nine-sided polygon.
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Decagon - A ten-sided polygon.
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Parallel lines are two lines in the same
plane that never intersect.
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| A plane is a flat, two-dimensional object. | A point specifies only location; it has
no length, width, or depth.  |
The radius of a circle is the distance
from the circle's center to a point on the circle, and is constant for
a given circle. |
A circle is the set of all points in a
plane that are equidistant from a given point in the plane.
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A circle's diameter is a segment that passes
through the center and has its endpoints on the circle. |
A ray can be thought of as a half a line.
It has a point on one end, and it extends infinitely in the other direction.  |
Congruent triangles are triangles that
have the same size and shape.
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A line has only one dimension: length.
It continues forever in two directions (so it has infinite length), but
it has no width at all.
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A line segment is the portion of a line
lying strictly between two points. It has a finite length and no width.  |
Solid Figures have length, width, and height.
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