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<$eometr\\
Geometry is the science which teaches the properties of
lines, angles, surfaces and solids.
A point indicates only position and has neither length,
breadth or thickness. A point has no magnitude.
A line has length, but no breadth or thickness ; it is either
straight, curved or mixed.
A straight line is the shortest distance between two points.
A curved line is continuously changing its position.
A mixed line is composed of straight and curved lines.
A. surface has length and breadth, but no thickness ; it may
be either plane or curved.
A solid has length, breadth, and thickness or depth.
An angle is the inclination of two lines which intersect or
meet each other. The point of intersection is called the vertex
of the angle. An angle is either right, acute or obtuse.
A right angle contains 90 degrees. An acute angle contains
less than 90 degrees. An obtuse angle contains more than 90
degrees.
Fig. 1.
Right Angle. Acute Angle. Obtuse Angle.
* Polygons.
Polygons are plane figures bounded on all sides by straight
lines, and are either regular or irregular, according to whether
their sides and angles are equal or unequal. The points at
which the sides meet are called vertices of the polygon. The
distance around any polygon is called the perimeter.
A figure bounded by three straight lines, forming three
angles, is called a triangle.
The sum of the three angles in any triangle, independent of
its size or shape, makes 180 degrees.
All triangles consist of six parts ; namely, three sides and
three angles. If three of these parts are known, one at least
being a side, the other parts may be calculated.
A triangle is called equilateral when all its three sides have
equal length. Then all the three angles are equal, namely, 60
degrees, because 60 X 3.= 180. (See Fig. 4).
* Some authorities define as polygons only figures having more than four sides.
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