Plane Geometry, Exam 1; Chapters 1.5-1.13

Angle

the figure formed by two straight lines drawn from the same point

Equal Angles can be called that when:

they can be made to coincide

Bisector of the angle

the line through the vertex of an angle which divides it into 2 equal angles

Perigon/round angle

when the line makes a complete revolution, 360 degrees

Straight Angle

an angle whose sides form one straight line extending through the vertex. 180 degrees

Adjacent Angles

two angles have the same vertex and a common side between them

Right Angles

when one straight line meets another so as to make two equal adjacent angles. 90 degrees

Perpendicular lines

when two lines form right angles with each other

Acute Angles

an angle that is less than a right angle

Obtuse Angle

an angle that is greater than a right angle

Reflex Angle

an angle that is greater than a straight angle but less than a perigon

Oblique Angles

angles other than a right or straight angle

Complementary Angles

their sum is a right angle

Supplementary Angles

their sum is a straight angle

Vertical Angles

when two straight lines intersect, and two angles are not adjacent

1 degree

60 minutes

1 minute

60 seconds

Protractor

the instrument used for measuring angles

Triangle

a figure bounded by three straight lines

vertices

intersection of the sides of an triangle

base

the side upon which a triangle is supposed to stand

Exterior angle of a triangle

an angle formed by one side of a triangle and the adjacent side extended through the vertex

Median of a triangle

the line drawn from any vertex to the midpoint of the opposite side

Altitude of a triangle

the perpendicular drawn from a vertex to the opposite side

Classification of triangles by sides

scalene, isosceles, equilateral

Scalene triangle

a triangle that has no two sides equal

Isosceles triangle

a triangle which has at least two sides equal

Equilateral triangle

a triangle that has all three sides equal

Classification of triangles by angles

acute, obtuse, right, equiangular

Acute triangle

a triangle which has three acute angles

Obtuse triangles

a triangle which has an obtuse angle

Right triangles

a triangle that has a right angle

Equiangular/Equilateral Triangles

a triangle which has three equal angles

Polygon

a plane figure bonded by straight lines

sides

lines of a polygon

vertices (polygon)

the intersections of a polygon

interior angle

angle formed by two consecutive sides of a polygon

exterior angle (polygon)

angle formed by one side of a polygon and the adjacent side extended

consecutive/ adjacent sides

two sides that meet at any vertex

Diagonal

a line joining two vertices that are not consecutive

Convex polygon

a polygon each of whose interior angles is less than 180 degrees

Concave polygon

a polygon with at least one interior angle greater than 180 degrees