polygons 9-4 warm up warm up lesson presentation lesson presentation problem of the day problem of...
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Polygons9-4
Warm UpWarm Up
Lesson PresentationLesson Presentation
Problem of the DayProblem of the Day
Lesson QuizzesLesson Quizzes
Polygons9-4
Warm Up
1. How many sides does a hexagon have?
2. How many sides does a pentagon have?
3. How many angles does an octagon have?
4. Evaluate (n – 2)180 for n = 7.
6
5
8
900
Polygons9-4
Problem of the Day
Jeffrey planted four carnations, three dahlias, seven marigolds, five cornflowers, one geranium, and four mums. He forgot to water them and on each of the two following days, half the remaining flowers died. How many flowers were still living at the end of the second day?6
Polygons9-4
MA.8.G.2.3 Demonstrate that the sum of the angles in a triangle is 180 degrees and apply this fact to find…the sum of angles in polygons.
Sunshine State Standards
Polygons9-4
Vocabularypolygon
regular polygon
trapezoid
parallelogram
rectangle
rhombus
square
Polygons9-4
A polygon is a closed plane figure formed by three or more segments. A polygon is named by the number of its sides.
Polygons9-4
nn-gon
8Octagon
7Heptagon
6Hexagon
5Pentagon
4Quadrilateral
3Triangle
Number of SidesPolygon
Polygons9-4
Additional Example 1A: Finding Sums of the Angle Measures in Polygons
Find the sum of the angle measures in a hexagon.
4 • 180° = 720°
4 triangles
Draw diagonals to divide the figure into triangles.
Polygons9-4
Additional Example 1B: Finding Sums of the Angle Measures in Polygons Continued
Find the sum of the angle measures in a octagon.
6 • 180° = 1080°
6 triangles
Draw diagonals to divide the figure into triangles.
Polygons9-4
Check It Out: Example 1
Find the sum of the angle measures in a heptagon.
5 • 180° = 900°
5 triangles
Draw diagonals to divide the figure into triangles.
Polygons9-4
The pattern is that the number of triangles is always 2 less than the number of sides. So an n-gon can be divided into n – 2 triangles. The sum of the angle measures of any n-gon is 180°(n – 2).
All the sides and angles of a regular polygon have equal measures.
Polygons9-4
Additional Example 2A: Finding the Measure of Each Angle in a Regular Polygon
Find the angle measures in the regular polygon.
8 congruent angles
8x° = 180°(8 – 2)
8x° = 180°(6)
8x° = 1080°
8x° 8
1080°8
=
x° = 135°
Polygons9-4
Additional Example 2B: Finding the Measure of Each Angle in a Regular Polygon
Find the angle measures in the regular polygon.
4 congruent angles
4y° = 180°(4 – 2)
4y° = 180°(2)
4y° = 360°
y° = 90°
4y° 4
360°4
=
Polygons9-4
Check It Out: Example 2
Find the angle measures in the regular polygon.
9 congruent angles
9y° = 180°(9 – 2)
9y° = 180°(7)
9y° = 1260°
9y°9
1260°9
=
y° = 140°
Polygons9-4
Quadrilaterals with certain properties are given additional names. A trapezoid has exactly 1 pair of parallel sides. A parallelogram has 2 pairs of parallel sides. A rectangle has 4 right angles. A rhombus has 4 congruent sides. A square has 4 congruent sides and 4 right angles.
Polygons9-4
Polygons9-4
Additional Example 3A: Classifying Quadrilaterals
quadrilateral
parallelogram
rectangle
rhombus
square
Four-sided polygon
2 pairs of parallel sides
4 right angles
4 congruent sides
4 congruent sides and 4 right angles
Give all the names that apply to the figure.
Polygons9-4
Additional Example 3B: Classifying Quadrilaterals
Give all the names that apply to the figure.
quadrilateral
parallelogram
rhombus
Four-sided polygon
2 pairs of parallel sides
4 congruent sides
Polygons9-4
Check It Out: Example 3A
Give all the names that apply to each figure.
Quadrilateral – 4 sided polygon Trapezoid – 1 pair of parallel sides
Polygons9-4
Give all the names that apply to each figure.
Quadrilateral – 4 sided polygon Parallelogram – 2 pairs of parallel sides Rhombus – 4 congruent sides
Check It Out: Example 3B
Polygons9-4
Standard Lesson Quiz
Lesson Quizzes
Lesson Quiz for Student Response Systems
Polygons9-4
Lesson Quiz: Part I
1. Find the sum of the angle measures in a
quadrilateral.
2. Find the sum of the angle measures in a
hexagon.
3. Find the measure of each angle in a regular
octagon.
360°
720°
135°
Polygons9-4
Lesson Quiz: Part II
4. Write all of the names that apply to the figure
below.
quadrilateral, rhombus, parallelogram
Polygons9-4
1. Identify the sum of the angle measures in a heptagon.
A. 520°
B. 540°
C. 720°
D. 900°
Lesson Quiz for Student Response Systems
Polygons9-4
2. Identify the sum of the angle measures in a 17-gon.
A. 1800°
B. 2700°
C. 3060°
D. 3600°
Lesson Quiz for Student Response Systems
Polygons9-4
3. Identify all the names that apply to the given figure.
A. parallelogram, rectangle
B. trapezoid, quadrilateral
C. rhombus, square, trapezoid
D. rectangle, quadrilateral, trapezoid
Lesson Quiz for Student Response Systems