6th Grade Math Textbook, Progress

Update your skills. See page 19.

Polygons

10-7

A

B C

D

E

L

M

O N

K

J

R

T

S

U

P

V

A diagonal of a polygon is a line segment

that connects two vertices and is nota side.

A
C
, A
D
, B
D
, B
E
,C
E
are diagonals of pentagon ABCDE.

Every pentagon, whether it is regular or

not regular, has five diagonals.

You can draw some of the diagonals of a polygon to help

you decide if the polygon is convex or concave.

convex polygon —cdiagonals do not have

any points outside the

polygon; JKLMNOis

a convex hexagon.

concave polygon — one or more diagonals

have points outside

the polygon; PRSTUV

is a concave hexagon.

Diagonal P
U
is outside

the hexagon.

triangle 3

quadrilateral 4

pentagon 5

hexagon 6

heptagon 7

octagon 8

nonagon 9

decagon 10

dodecagon 12

Polygon Number of Sides

In general, if a polygon has nsides, you call it an n-gon.

A polygon of 16 sides is a 16-gon.

A polygon is a closed plane figure made up of line segments that

intersect only at their endpoints and in such a way that no two segments

are on the same line. You can classify a polygon by its number of sides.

When all of the sides of a

polygon are congruent and all

of the angles are congruent, the

polygon is a regular polygon.

Polygons

regular

triangle

regular

quadrilateral

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