1. Splash Screen

2. Five-Minute Check (over Lesson 11–1) NGSSS Then/Now New Vocabulary
Key Concept: Area of a Trapezoid
Example 1: Real-World Example: Area of a Trapezoid
Example 2: Standardized Test Example
Key Concept: Area of a Rhumbus or Kite
Example 3: Area of a Rhombus and a Kite
Example 4: Use Area to Find Missing Measures
Concept Summary: Areas of Polygons
Lesson Menu

3. Find the perimeter of the figure
Find the perimeter of the figure. Round to the nearest tenth if necessary.
A. 48 cm
B. 56 cm
C cm
D. 110 cm A B C D
5-Minute Check 1

4. Find the perimeter of the figure
Find the perimeter of the figure. Round to the nearest tenth if necessary.
A ft
B. 40 ft
C ft
D. 45 ft A B C D
5-Minute Check 2

5. Find the area of the figure. Round to the nearest tenth if necessary.
A. 58 in2
B. 83 in2
C in2
D. 180 in2 A B C D
5-Minute Check 3

6. Find the area of the figure. Round to the nearest tenth if necessary.
A. 90 m2
B. 62 m2
C. 5 m2
D. 3.4 m2 A B C D
5-Minute Check 4

7. Find the height and base of the parallelogram if the area is 168 square units.
A. 11 units; 13 units
B. 12 units; 14 units
C. 13 units; 15 units
D. 14 units; 16 units A B C D
5-Minute Check 5

8. The area of an obtuse triangle is 52. 92 square centimeters
The area of an obtuse triangle is square centimeters. The base of the triangle is 12.6 centimeters. What is the height of the triangle?
A. 2.1 centimeters
B. 4.2 centimeters
C. 8.4 centimeters
D centimeters A B C D
5-Minute Check 6

9. MA.912.G.2.5 Explain the derivation and apply formulas for perimeter and area of polygons.
MA.912.G.2.6 Use coordinate geometry to prove properties of congruent, regular and similar polygons, and to perform transformations in the plane.
NGSSS

10. You found areas of triangles and parallelograms. (Lesson 11–1)
Find areas of trapezoids.
Find areas of rhombi and kites.
Then/Now

11. height of a trapezoid
Vocabulary

12. Concept 1

13. Area of a Trapezoid
SHAVING Find the area of steel used to make the side of the razor blade shown below.
Area of a trapezoid
h = 1, b1 = 3, b2 = 2.5
Simplify.
Answer: A = 2.75 cm2
Example 1

14. A B C D Find the area of the side of the pool outlined below.
A. 288 ft2
B ft2
C ft2
D. 310 ft2 A B C D
Example 1

15. OPEN ENDED Miguel designed a deck shaped like the trapezoid shown below. Find the area of the deck.
Read the Test Item
You are given a trapezoid with one base measuring 4 feet, a height of 9 feet, and a third side measuring 5 feet. To find the area of the trapezoid, first find the measure of the other base.
Example 2

16. Solve the Test Item
Draw a segment to form a right triangle and a rectangle. The triangle has a hypotenuse of 5 feet and legs of ℓ and 4 feet. The rectangle has a length of 4 feet and a width of x feet.
Example 2

17. Use the Pythagorean Theorem to find ℓ.
a2 + b2 = c2 Pythagorean Theorem
42 + ℓ2 = 52 Substitution
16 + ℓ2 = 25 Simplify.
ℓ2 = 9 Subtract 16 from each side.
ℓ = 3 Take the positive square root of each side.
Example 2

18. Answer: So, the area of the deck is 30 square feet.
By Segment Addition, ℓ + x = 9. So, 3 + x = 9 and x = 6. The width of the rectangle is also the measure of the second base of the trapezoid.
Area of a trapezoid
Substitution
Simplify.
Answer: So, the area of the deck is 30 square feet.
Example 2

19. Check
The area of the trapezoid is the sum of the areas of the areas of the right triangle and rectangle. The area of the triangle is or 6 square feet. The area of the rectangle is (4)(6) or 24 square feet. So the area of the trapezoid is or 30 square feet.
Example 2

20. Ramon is carpeting a room shaped like the trapezoid shown below
Ramon is carpeting a room shaped like the trapezoid shown below. Find the area of the carpet needed.
A. 58 ft2
B. 63 ft2
C. 76 ft2
D. 88 ft2 A B C D
Example 2

21. Concept 2

22. A. Find the area of the kite.
Area of a Rhombus and a Kite
A. Find the area of the kite.
Area of a kite
d1 = 7 and d2 = 12
Answer: 42 ft2
Example 3A

23. B. Find the area of the rhombus.
Area of a Rhombus and a Kite
B. Find the area of the rhombus.
Step 1 Find the length of each diagonal.
Since the diagonals of a rhombus bisect each other, then the lengths of the diagonals are or 14 in. and or 18 in.
Example 3B

24. Step 2 Find the area of the rhombus.
Area of a Rhombus and a Kite
Step 2 Find the area of the rhombus.
Area of a rhombus
d1 = 14 and d2 = 18
Simplify. 2
Answer: 126 in2
Example 3B

25. A B C D A. Find the area of the kite. A. 48.75 ft2 B. 58.5 ft2
C ft2
D. 117 ft2 A B C D
Example 3A

26. A B C D B. Find the area of the rhombus. A. 45 in2 B. 90 in2
C. 180 in2
D. 360 in2 A B C D
Example 3B

27. Use Area to Find Missing Measures
ALGEBRA One diagonal of a rhombus is half as long as the other diagonal. If the area of the rhombus is 64 square inches, what are the lengths of the diagonals?
Step 1 Write an expression to represent each measure. Let x represent the length of one diagonal. Then the length of the other diagonal is x. __ 1 2
Example 4

28. Step 2 Use the formula for the area of a rhombus to find x.
Use Area to Find Missing Measures
Step 2 Use the formula for the area of a rhombus to find x.
Area of a rhombus
A = 64, d1= x, d2= x
__  1 2
Simplify.
256 = x2 Multiply each side by 4.
16 = x Take the positive square root of each side.
Example 4

29. Use Area to Find Missing Measures
Answer: So, the lengths of the diagonals are 16 inches and (16) or 8 inches. __ 1 2
Example 4

30. Trapezoid QRST has an area of 210 square yards. Find the height of QRST.
A. 3 yd
B. 6 yd
C. 2.1 yd
D. 7 yd A B C D
Example 4

31. Concept 3

32. End of the Lesson