1. CIRCUMFERENCE AND AREA
OF CIRCLES
LESSON 21

2. LETS REVIEW Perimeter of a Square P = 4s Area of a Square A= s2
Perimeter of a Rectangle
P = 2L + 2W
Area of a Rectangle
A= LW or Bh

3. LETS REVIEW bh 2 A = Perimeter of a Parallelogram P = 2b + 2s
Area of a Parallelogram
A= bh
Perimeter of a Triangle
P = s + s + s bh 2
Area of a Triangle
A =

4. LETS REVIEW h(a+b) 2 A= Perimeter of a Trapezoid P = s + s + s + s
Area of a Trapezoid A=

5. EXAMPLE 1 Circumference of a Circle Area of a Circle
Find the circumference and area of the figure.
Circumference of a Circle
C = 3.14(10)
C = 31.4 cm
Area of a Circle
A = 3.14(5)2
A = 3.14(25)
A = 78.5 cm2
Radius is half the diameter

6. YOU TRY!
Find the circumference and area of the figure.
3 mm

7. SOLUTION Circumference of a Circle Area of a Circle
Find the circumference and area of the figure.
Circumference of a Circle
C = 3.14(6)
C = mm
3 mm
Area of a Circle
A = 3.14(3)2
A = 3.14(9)
A = mm2
Diameter is twice the radius

8. EXAMPLE 2 Area of Big Circle Area of a Small Circle
Find the area of the shaded figure.
Area of Big Circle
A = 3.14(10)2
A = 3.14(100)
A = 314 cm2
Area of a Small Circle
Area of Shaded Region
Big Circle - Small Circle
cm2
A = 3.14(4)2
A = 3.14(16)
A = cm2

9. YOU TRY! Area of Big Circle Area of a Small Circle
Find the area of the shaded figure.
Area of Big Circle
Area of a Small Circle
Area of Shaded Region

10. SOLUTION Area of Big Circle Area of a Small Circle
Find the area of the shaded figure.
Area of Big Circle
A = 3.14(5)2
A = 3.14(25)
A = 78.5 mm2
Area of a Small Circle
Area of Shaded Region
Big Circle - Small Circle
65.94 mm2
A = 3.14(2)2
A = 3.14(4)
A = mm2

11. Class work Check solutions to Lesson 20
Copy notes and examples to Lesson 21
Do Lesson 21 worksheet