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# H Geom chap 1 vocab

TermDefinition
undefined a figure that can't be defined (described) by using other figures Point, Line, Plane
point a location that has no size, represented as a dot
line a straight line that has no thickness and extends, both directions, to infinity (forever)
plane a flat surface that has no thickness and extends in all directions to infinity (forever)
collinear points that lie on the same line
coplanar points that lie on the same plane
noncoplanar points that do not lie on the same plane
segment (line segment) part of a line consisting of two points and all the points in between them
endpoint a point at one end of the segment or the starting point of a ray
ray a part of a line that starts at an endpoint and extends forever (infinity) in one direction
opposite rays two rays that share a common endpoint and form a line
postulate (axiom) a statement that is accepted as true without proof--describes geometric properties
coordinate of a point a pair of numbers that define it's exact location on a 2-dimensional plane---(x,y)
distance absolute value of the difference of the coordinates
length distance between A and B on a line, segment, or ray
congruent segments segments that have the same length
construction a way of creating a figure that is more precise--one way use a compass and straightedge
between 3 points lie on the same line (collinear), the point that lies in the middle of the other two
midpoint the point that divides a segment into two congruent segments
bisects divides into 2 equal pieces
segment bisector any ray, segment, or line that intersects a segment at its midpoint
angle a figure formed by two rays or sides, with a common endpoint
vertex (vertices) common endpoint(s)
interior of an angle set of all points inside the sides of the angle
exterior of an angle set of all points outside the sides of the angle
measure find the size, amount, or degree of something using an instrument or device marked in a standard unit
degree unit of measure for a circle which represents 1/360th of the circle
acute angle angle that measures greater than 0* and less than 90* , so 0*-90*
right angle measures exactly 90*
obtuse angle angle that measures greater than 90* and less than 180* , so 90*-180*
straight angle 2 opposite rays that measure 180*
congruent angles angles that have the same measure
angle bisector a ray that divides an angle into 2 congruent angles
adjacent angles 2 angles in the same plane with a common vertex and a common side
linear pair of angles pair of adjacent angles whose noncommon sides are opposite rays (form a line)
complementary angles 2 angles whose measures have a sum of 90*
supplementary angles 2 angles whose measures have a sum of 180*
vertical angles 2 nonadjacent angles formed by 2 intersecting lines (angles directly across from each other)
perimeter the sum of all the side lengths of a figure
area number of nonoverlapping square units that exactly cover the figure
base any side of a triangle
height segment from a vertex that forms a right angle with a base (from a triangle)
diameter segment whose endpoints are on a circle and passes through the center of the circle
radius segment whose endpoints are on the circle and the center of the circle
circumference distance around the circle
pi ratio of a circle's circumference to its diameter (same for all circles--about 3.14 or 22/7)
coordinate plane plane that is divided into four regions by a horizontal line (x-axis) and a vertical line (y-axis)
legs 2 sides that form the right angle of a triangle
hypotenuse side across from the right angle of a triangle
transformation change in position, size, or shape of a figure--translation, dilation, reflection, rotation
preimage original figure-before a transformation
image figure after a transformation from an original
reflection transformation across a line (line of reflection) ---flip
rotation transformation about a point P (center of rotation) ---turn
translation transformation in which all the points of a figure move the same distance in the same direction----slide
coordinate a point that corresponds to one and only one number on the ruler
Created by: rachel schmelzer