1. 11-4 Areas of Regular Polygons and Composite Figures
You used inscribed and circumscribed figures and found the areas of circles.
Find areas of regular polygons.
Find areas of composite figures.

2. Regular Polygon A regular polygon is both equilateral and equiangular.
Equilateral—all sides are the
same length.
Equiangular—all angles are
the same measure.

3. Classify each polygon as equilateral, equiangular and/or regular.

4. Regular Polygon Parts
The center of a regular polygon is the point of intersection of the perpendicular bisectors of the sides.
center

5. Regular Polygon Parts
The segment from a vertex to the center is the radius.
radius

6. Regular Polygon Parts
The perpendicular segment from the center to a side is an apothem (AP uh them).
center
apothem

7. All of the radii of a regular polygon are congruent
All of the radii of a regular polygon are congruent. Any regular polygon can be divided into congruent isosceles triangles.
To find the area, you could then find the area of these triangles.
OR….

8. Central Angle

9. In the figure, pentagon PQRST is inscribed in Identify the center, a radius, an apothem, and a central angle of the polygon. Then find the measure of a central angle.
center: point X
radius: XR or XQ
apothem: XN
central angle: RXQ
A pentagon is a regular polygon with 5 sides. Thus, the measure of each central angle of pentagon PQRST is or 72.
Answer: mRXQ = 72°

10. In the figure, hexagon ABCDEF is inscribed in Find the measure of a central angle.
A. mDGH = 45°
B. mDGC = 60°
C. mCGD = 72°
D. mGHD = 90°

11. Step 2 Find the area of one triangle.
FURNITURE The top of the table shown is a regular hexagon with a side length of 3 feet and an apothem of 1.7 feet. What is the area of the tabletop to the nearest tenth?
Step 1 Since the polygon has 6 sides, the polygon can be divided into 6 congruent isosceles triangles, each with a base of 3 ft and a height of 1.7 ft.
Step 2 Find the area of one triangle.
b = 3 and
h = 1.7
Step 3 Multiply the area of one triangle by the total number of triangles.
= 2.55 ft2
Simplify.
Since there are 6 triangles, the area of the table is ● 6 or 15.3 ft2.
Answer: 15.3 ft2

12. UMBRELLA The top of an umbrella shown is a regular hexagon with a side length of 2 feet and an apothem of 1.5 feet. What is the area of the entire umbrella to the nearest tenth?
A. 6 ft2
B. 7 ft2
C. 8 ft2
D. 9 ft2

13. Use the Regular Polygon Theorem
The area of a regular polygon is one-half the product of its perimeter and its apothem.
A = ½ap
p. 808

14. Find the area of the regular pentagon.
a = 6.9 in
A pentagon has ___ sides.
The perimeter is ___.
Area = ½ (apothem)(perimeter)
A = ½(6.9)(50)
A = in.2 5 50

15. Find the area of a regular octagon
An octagon has ___ sides.
The perimeter is ___.
Area = ½ (apothem)(perimeter)
A = ½(18.1)(120)
A = 1086 cm.2 8
a = 18.1 cm
15cm
120

16. A. Find the area of the regular hexagon. Round to the nearest tenth.
Step 1 Find the measure of a central angle.
A regular hexagon has 6 congruent central angles, so
Step 2 Find the apothem.
Apothem PS is the height of isosceles ΔQPR. It bisects QPR, so mSPR = It also bisects QR, so SR = 2.5 meters.
ΔPSR is a 30°-60°-90° triangle with a shorter leg that measures 2.5 meters, so

17. Step 3 Use the apothem and side length to find the area.
Area of a regular polygon
≈ 65.0 m Use a calculator.
Answer: about 65.0 m2

18. Composite Figures
A composite figure is a figure that can be separated into regions that are basic figures, such as triangles, rectangles, trapezoids, and circles.
To find the area of a composite figure, find the area of each basic figure and then use the Area Addition Postulate.

19. POOL The dimensions of an irregularly shaped pool are shown
POOL The dimensions of an irregularly shaped pool are shown. What is the area of the surface of the pool?
The figure can be separated into a rectangle with dimensions 16 feet by 32 feet, a triangle with a base of 32 feet and a height of 15 feet, and two semicircles with radii of 8 feet.
Area of composite figure 
Answer: The area of the composite figure is square feet to the nearest tenth.

20. Find the area of the figure in square feet
Find the area of the figure in square feet. Round to the nearest tenth if necessary.
A ft2
B ft2
C ft2
D ft2

21. Find the area of the shaded figure.
To find the area of the figure, subtract the area of the smaller rectangle from the area of the larger rectangle. The length of the larger rectangle is or 150 feet. The width of the larger rectangle is or 70 feet.
A of shaded figure = A of larger rectangle – A of smaller rectangle
Area formulas
Substitution
Simplify.
Simplify.
Answer: The area of the shaded figure is 8500 square feet.

22. INTERIOR DESIGN Cara wants to wallpaper one wall of her family room
INTERIOR DESIGN Cara wants to wallpaper one wall of her family room. She has a fireplace in the center of the wall. Find the area of the wall around the fireplace.
A. 168 ft2
B. 156 ft2
C. 204 ft2
D. 180 ft2

23. Assignment 11-4
Page 811, 8-12, 15-16, 19
No formulas with numbers, no credit.