plane surfaces
Set of points on a plane that describes an area
of space.
parts of a circle
Circle: closed
plane curve; all its points are the same distance from a fixed
point (center).
quadrant
Quarter of a
circle’s circumference; it corresponds to an arc of 90°.
center
Point located at
the same distance from every point on the circle’s
circumference.
arc
Section of a
circle between two points on the circle.
radius
Line that joins a
point on a circle’s circumference to its center; it is one half
of the diameter.
sector
Surface bounded by
two radii and an arc of a circle.
diameter
Line that connects
two points on a circle’s circumference and passes through its
center.
semicircle
A half circle that
is delimited by its diameter.
circumference
Length of a circle
that corresponds to the product of its diameter and pi.
examples of angles
Angle: figure formed by two intersecting lines
or planes; it is measured in degrees.
45°
reentrant angle
Angle between 180° and 360°.
obtuse angle
Angle between 90° and 180°.
right angle
Angle formed by two lines or two perpendicular
planes that measures 90°.
acute angle
Angle that is smaller than a right angle (less
than 90°).
360°
240°
130°
90°
0°
polygons [1]
Geometric plane figures with several sides and a
number of equal angles.
![polygons [1]](http://visual.merriam-webster.com/images/science/scientific-symbols/geometrical-shapes/polygons_1.jpg "polygons [1] image")
cylinder
Volume or solid generated by the rotation of a
straight line (generatrix) moving along a curved
line (directrix).
regular octahedron
Volume or solid with eight triangular sides of
equal area; it has six vertices and 12 edges.
parallelepiped
Volume or solid with six sides (parallelograms)
that are parallel in pairs.
cube
Volume or solid with six square sides of equal
area and six equal edges; it has eight vertices.
pyramid
Volume or solid generated by straight lines
(edges) connecting the angles of a polygon
(base) to the vertex and whose sides form
triangles.
cone
Volume or solid generated by the rotation of a
straight line (generatrix) along a circular line
(directrix) from a fixed point (vertex).
torus
Volume or solid generated by the rotation of a
circle at an equal distance from its center of
rotation.
sphere
Volume with all the points on its surface the
same distance from its center; the solid thus
delimited is a round ball.
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![polygons [2]](http://visual.merriam-webster.com/images/science/scientific-symbols/geometrical-shapes/polygons_2.jpg "polygons [2] image")
![polygons [3]](http://visual.merriam-webster.com/images/science/scientific-symbols/geometrical-shapes/polygons_3.jpg "polygons [3] image")
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