21.4 Areas of Circles p. 466

21.4 Areas of Circles

p. 466

WHAT IS THE AREA OF ONE CIRCULAR RUG?*Remember - area is the number of SQUARE units it takes to cover an area

RECAP: Match the formula with its corresponding shape

• PARALLELOGRAMS

• TRAPEZOIDS

• RIGHT TRIANGLES

• “OTHER” TRIANGLES

• SQUARES

• RECTANGLES

• A = lw

• A = 1/2 bh

• A = s2

• A = bh

• A = 1/2 (b1 + b2)

21.4 Areas of Circles

p. 466

Introduction: Quick Review Objective: to learn to use a formula to find the area of a circle Formula: Area of a Circle A = r Example: Draw a circle with a 3 inch radius, label it and use the formula to calculate the area in yourjournal

Glossary

2

Circle Song

Guided Instruction: Example 1: use 22/7 for A = r

A =

A =

A =

A =

A = ft

2

2

Guided Instruction: Example 2: use 3.14 for A = r

A =

A =

A = m

2

2

4.6 m

Check for Understanding:

Group Bag ActivityObjective: Calculate the area of each of your three objects in your bag. Use string and a ruler to accurately measure the radius. Show your work on the recording sheet included in your bag. Raise your hand when finished. Work cooperatively with your group and allow everyone to have a part in measuring and calculating area. Remember: A = r 2

Recording Sheet:Circular object 1/2 of a circle type object “approximately” 1/4 of a circle type object

Formula and Work: Formula and Work: Formula and Work:

area: ______ (include your unit of measurement squared - cm, in.?)

area: ______ (include your unit of measurement squared - cm, in.?)

area: ______ (include your unit of measurement squared - cm, in.?)