9.2 Curves, Polygons, and Symmetry

MATH 202

simple curve

curve that does not intersect itself, can start and stop at the same place but it doesn’t have to

closed curve

a curve that must start and stop at the same place, can intersect itself but it doesn’t have to

polygon

a simple, closed curve with sides that are line segments, no curves

vertex

a point on a polygon where two lines meet

convex

a simple closed curve is this if the segment containing any two points on the curve is contained in the curve

concave

a simple closed curve is this if at least one segment connecting two points on the curve crosses into the exterior of the curve

triangle

has 3 sides

quadrilateral

has 4 sides

pentagon

has 5 sides

hexagon

has 6 sides

heptagon

has 7 sides

octagon

has 8 sides

nonagon

has 9 sides

decagon

has 10 sides

regular polygons

convex polygons in which all interior angles are congruent and all sides are congruent

right

one right angle 90 degrees

acute

all 3 acute angles, 60 degrees each

obtuse

one obtuse angle

scalene

no congruent sides

equilateral

all congruent sides

isosceles

at least 2 congruent sides

trapezoid

at least one set of parallel lines

isosceles trapezoid

congruent base angles

kite

2 pairs of adjacent congruent sides

parallelogram

2 sets of parallel lines

rectangle

parallelogram with 90 degree angles or right angles

square

rectangle with congruent sides

rhombus

all congruent sides but not right angles

line symmetry

a figure has a line of symmetry if it is its own image under the reflection of the line

rotational symmetry

when the figure can be rotated less than 360 degrees about some point so that it matches the original figure

point symmetry

a figure that has 180 degree rotational symmetry