+ Bell WorkSolve

25 ⅚ -18 ⅜

5 ⅛ + 7 ⅘

+ Bell Work Answer25 ⅚ -18 ⅜

25 20/24 – 18 9/247 11/24

5 ⅛ + 7 ⅘5 5/40 + 7 32/40

12 37/40

+

Lesson 3: Perimeter and Circumference

+

What is a perimeter?

+

Perimeter*The distance around an

object.

+Find the perimeter of this object

+

Answer:28 Units

+Find the perimeter of the object

+

Answer:44 Units

+Every point on a circle is the same distance from the center of the circle. This distance is called the radius.Radius*: The straight line from the center of the circle to the outer edge.

+Diameter*: Twice the length of the radius of a circle.

+Circumference*: The perimeter of a circle.

+Many ancients thought that the circle was the perfect geometric figure. They were especially interested in the relationship between the diameter of a circle and the circumference of the same circle. They found that it takes approximately 3.14 diameters to go all the way around a circle no matter how small or large the circle is.

+We now know the exact number of times the diameter will go around a circle. This exact number is a number is a number we call pi (pronounced pie). We represent pi with the symbol π.

+π is an infinite number meaning that it will go on and on forever. This also means that it is an irrational number. A calculator gives a decimal approximation of π as 3.141592654.(In the book, 3.14 will be used as an approximation for pi when doing calculations.)

+It takes π diameters to equal the circumference of a circle.Circumference = πD

+It takes 2π radii to equal the circumference of a circle. Circumference = 2πr

+Example:The radius of a circle is 3 cm. Find the circumference of the circle.

+Answer:Circumference = 2πr

= 2π(3 cm)= 2(3.14)(3 cm)= 18.84 cm

+Example:The circumference of a circle is 24 meters. Find the radius of the circle.

+Answer:Circumference = 2πr

24 m = 2πr 24 m = 2(3.14)(r) 24 m = 6.28r r = 3.82m

+Find the perimeter of the figure

+

Answer:Perimeter = 10 ft +10 ft + 8 ft + (2π(4 ft)/2) = 28 ft + (2(3.14)(4 ft)/2)

= 28 ft + 12.56 ft = 40.56 ft

+Practice:The length of a rectangle is 10 cm. The width of the rectangle is 5 cm. Find the perimeter of the rectangle.

+Practice:The perimeter of a square is 12 meters. What is the length of one side of the square?

+

Practice:The radius of a circle is 5 inches. Find the circumference of the circle.

+

HW: Lesson 3 #1-30Due Tomorrow