# Basic Geometry terms

### 48 terms by dcdavis66

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ALE Geometry

### acute triangle

a triangle whose interior angles are all acute

### altitude

the perpendicular distance from the base of a geometric figure to opposite vertex (or side if parallel)

### complementary angles

two angles whose measures have a sum of 90 degrees

### congruent

having the same size and shape

### edge

the line segment where two faces of a solid figure meet

### equilateral triangle

a triangle with three congruent sides

### perpendicular lines

lines that intersect at one point and form right angles

### perimeter

the distance around a 2-dimensiional figure

### area

the number of square units needed to cover a surface

### right angle

an angle with a measure of 90 degrees

### straight angle

an angle whose measure is 180 degrees

### obtuse angle

an angle with a measure of more than 90 degrees but less than 180 degrees

### acute angles

angles that measures greater than 0 degrees and less than 90 degrees

### exterior angles

angles on the outer sides of two lines cut by a transversal

### face

a flat surface of a polyhedron

### hypotenuse

in a right triangle, the side opposite the right angle

### interior angles

angles on the inner sides of two lines that cut by a transversal

### intersecting lines

two lines that cross at exactly one point

### isosceles triangle

a triangle with two congruent sides

### line

a straight path that extends infinitely in opposite directions

### line segment

part of a line with two endpoints

### line symmetry

a type of symmetry in which a line divides a figure into two congruent parts that are mirror images

### obtuse triangle

a triangle with one obtuse angle

### parallell lines

two lines in the same plane that never intersect

### parallelogram

a quadrilateral with opposite sides parallel and congruent

### perpendicular bisector

line that intersects a line segment at its midpoint and forms right angles

### plane

a flat surface that extends infinitely in all directions

### polygon

a closed plane figure made of line segments

### prism

a polyhedron with two parallel, congruent bases; all other faces of the prism are parallelograms

### pyramid

a 3-dimensional shape whose base is a polygon and whose triangular faces meet at a single point

### Pythagorean Theorem

the square of the hypotenuse (c) of a right triangle is equal to the sum of the squares of the legs (a and b)

a four-sided polygon

a line segment with one endpoint at the center of a circle and the other endpoint on the circle

### ray

part of a line that has one endpoint and extends forever in the other direction

### reflection

a transformation that produces a mirror image of a geometric figure (flip)

### regular polygon

a polygon in which all sides are the same length and all angles have the same measure

### rhombus

a parallellogram whose four sides are congruent and whose opposite angles are congruent

### supplementary angles

two angles whose sum equals 180 degrees

### sphere

a three-dimensional shape with all points on the surface equidistant from the center

### scalene triangle

a triangle with no congruent sides

### rotation

a transformation of a figure by turning it about a fixed point called the center of rotation or axis

### right triangle

a triangle with one right angle

### tessellation

a pattern of congruent shapes covering a surface without gaps or overlap

### transformation

a change in size, shape, of position of a geometric figure

### translation

a transformation that moves a geometric figure by sliding each of the points the same distance in the same direction

### vertex

a point where 2 rays meet, where two sides of a polygon meet or where the edges of a polyhedron meet; the top point of a cone or pyramid

### vertical angles

a pair of opposite congruent angles formed by two intersecting lines

### volume

the number of cubic units needed to fill the space occupied by a solid

### Flickr Creative Commons Images

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