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Basic Geometric Terms
Definition Example
Point – an exact location in space. A point has no dimension.
(read “point A”)
Line – a collection of points along a straight path that extends endlessly in both directions. ᠩᠨ㎂䙒䙒䙒䙒ጘ^ (read “line CB”)
Line Segment – a part of a line having two endpoints. (^) ᠧᠨ㍤㍤㍤㍤ (^) (read “line segment ᠧᠨ”)
The length of ᠧᠨ㍤㍤㍤㍤^ is denoted ᠧᠨ.
Ray – a part of a line having only one endpoint. ᠩᠰ䙒䙒䙒䙒䙒ጘ^ (read “ray ᠩᠰ”) The endpoint is always the first letter.
Angle – consists of two rays that have a common endpoint called the vertex of the angle. ᔅᠧᠨᠩ (read “angle ᠧᠨᠩ”) The vertex is always the middle letter. ᔅᠧᠨᠩ can also be written as ᔅᠩᠨᠧ or just ᔅᠨ.
Plane – a flat surface that extends endlessly in all directions.
Plane ᠧᠨᠩᠰ
Straight Angle – an angle whose measure is 180°. ᔅᠧᠨᠩ is a straight angle.
Right Angle – an angle whose measure is 90°.
ᔅᠰᠱᠲ is a right angle.
A
C B
A B
C D
A B
C
Vertex
A
B C
D
A B (^) C
D
E (^) F
Symbol for right angle
Acute Angle – an angle whose measure is less than 90°.
ᔅᡐᡑᡒ is an acute angle.
Obtuse Angle – an angle whose measure is more than 90° and less than 180°.
ᔅᠩᠰᠱ is an obtuse angle.
Two angles are complementary if the sum of their measures is 90°. ᡥᔅᠧ ㎗ ᡥᔅᠨ 㐄 25 ° ㎗ 65 ° 㐄 90 ° ᔅᠧ and ᔅᠨ are complementary angles.
Two angles are supplementary if the sum of their measures is 180°. ᡥᔅᠩ ㎗ ᡥᔅᠰ 㐄 40 ° ㎗ 140 ° 㐄 180 ° ᔅᠩ and ᔅᠰ are supplementary angles.
Intersecting Lines – two lines that cross.
ᠧᠩ㎂䙒䙒䙒䙒ጘ^ intersects ᠰᠱ㎂䙒䙒䙒䙒ጘ^ at point ᠨ.
Parallel Lines – two lines in the same plane that do not intersect.
ᠱᠲ㎂䙒䙒䙒䙒ጘ^ ᔐ ᠳᠴ㎂䙒䙒䙒䙒ጘ^ is read “ᠱᠲ㎂䙒䙒䙒䙒ጘ^ is parallel to ᠳᠴ㎂䙒䙒䙒䙒ጘ.”
Perpendicular Lines – two lines that intersect to form right angles.
ᡄᡆ㎂䙒䙒䙒䙒ጘ^ ᘵ ᡂᡃ㎂䙒䙒䙒䙒ጘ^ is read “ᡄᡆ㎂䙒䙒䙒䙒ጘ^ is perpendicular to ᡂᡃ㎂䙒䙒䙒䙒ጘ.” ᔅᡄᡅᡂ, ᔅᡄᡅᡃ, ᔅᡂᡅᡆ, and ᔅᡃᡅᡆ are all right angles.
Vertical Angles – two angles with equal measure formed by two intersecting lines.
ᔅᠨᠧᠱ and ᔅᠰᠧᠩ are vertical angles. ᔅᠨᠧᠰ and ᔅᠱᠧᠩ are vertical angles.
X
Y (^) Z
C
D (^) E
A 25°^ B 65°
D
40°^ 140° C
A B
C
D
E
E F
G H
P Q
R
S
T
B
C
D
E
A
120°
120°
6 0° 6 0°
