polygons can be concave or convex convex concave
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Polygons can be CONCAVE or CONVEX
CONVEX
CONCAVE
Concave and ConvexPolygons
If a polygon has an indentation (or cave), the polygon is called a concave polygon. Any polygon that does not have an indentation is called a convex polygon.
Any two points in the interior of a convex polygon can be connected by a line segment that does not cut or cross a side of the polygon.
Concave polygon Convex polygon
We will only be discussing CONCAVE polygons
Triangle
Quadrilateral
Pentagon
Hexagon
Heptagon
Octagon
Nonagon
Decagon
Dodecagon
n-gonHendecagon
F
A B
C
DE
Important TermsA VERTEX is the point of intersection of two sides
A segment whose
endpoints are two
nonconsecutive vertices is
called a DIAGONAL.
CONSECUTIVE VERTICES are two endpoints of any side.
Sides that share a vertex are called CONSECUTIVE SIDES.
Tear off two vertices….
Line up the 3 angles (all vertices touching)
A straight line = 180°
Angle sum of a Triangle 180° <1 + <2 + <3 = 180°
1
2
3
ALWAYS!!!
Consider a Quadrilateral What is the angle sum?
<1 + <2 + <3 + <4 = ?
Quadrilateral Draw a diagonal…what do you
get?
Two triangles
1
2 3
4
5
6
Quadrilateral Each triangle = 180°
Therefore the two triangles together = 360°
1
2 3
4
5
6
180°
180°
Angle sum of a Quadrilateral 180° + 180° =
360°
Consider a Pentagon What is the angle sum?
Pentagon Draw the diagonals from 1 vertex
How many triangles?
Angle sum of a Pentagon Draw the diagonals from 1 vertex
180°
180°
180°
Continue this process through Decagon Draw the diagonals from 1 vertex
Continue this process through Decagon Draw the diagonals from 1 vertex
What about a 52-gon?
What is the angle sum?
Can you find the pattern?
1 180°
2 360°
3 540°
4 720°
5 900°
6 1080°
Find the nth term
7 1260°
8 1440°
n - 2 (n – 2)(180)
m1 =
1
2
3
110
(5x - 5)
(4x + 15)
(8x - 10)
pentagon
5x - 5 + 4x + 15 + 8x - 10 + 110 + 90 =
54017x + 200= 540 -200 -200
17x = 340
x = 20 17 17
5(20) - 5
= 95
Find m1.
More important terms
Exterior Angles
Interior Angles
the SUM of an interior angle and it’s corresponding exterior angle = 180o
Sum of Interior Angles =
Sum of Interior & Exterior Angles =
180
12
34
5 6
180
180
180
540
Sum of Exterior Angles =
360 540- 180=
Sums of Exterior Angles
180•3 = 540
180
180
180
180
Sum of Interior Angles =
Sum of Interior & Exterior Angles =
360 720
Sum of Exterior Angles =
360 720- 360=
Sums of Exterior Angles
180•4 = 720
Sums of Exterior Angles
Sum of Interior & Exterior Angles =Sum of Interior Angles =
Sum of Exterior Angles =
180•5 =
180•3 =
900
540
900- 540=360
What conclusion can you come up with regarding the exterior angle sum of a CONVEX n-polygon??
Sum of Interior & Exterior Angles =Sum of Interior Angles =
Sum of Exterior Angles =
180n
180(n-2) = 180n - 360
180n – (180n – 360)
The exterior angle sum of a CONVEX polygon =
360°
Important Terms
EQUILATERAL - All sides are congruentEQUIANGULAR - All angles are congruentREGULAR - All sides and angles are congruent
Interior Angle Measure of a REGULAR polygons
60° 90°
Equilateral Triangle Angle measure = 60°
Square Angle measure = 90°
These are measurement that we generally know at this time,
But what about the other regular polygons?
How do we calculate the interior angle measure?
Pentagon
108°
108°
108°
108°
108° 72°
72°
72°
72°
72°
Interior Angle Measure of a REGULAR polygons
108°
120°
135°
Calculate by:
Angle Sum
Number of sides
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