Circle Formulas: Circumference and Area

Grade 7 Mathematics 15-minute lesson

What Are We Measuring?

Look at this circular plate String around the edge = ? Space it covers on table = ?

Key Vocabulary

Circumference: The distance around the outside of a circle Area: The amount of space inside a circle Radius (r): Distance from center to edge Diameter (d): Distance across the circle through center

Circle Formulas

Let's Calculate Together

Given: Circle with radius = 3 units Circumference: C = 2πr = 2 × π × 3 = 6π ≈ 18.85 units Area: A = πr² = π × 3² = 9π ≈ 28.27 square units

Think About This...

How do you think the circumference and area formulas are connected? Write your thoughts on your mini whiteboard What patterns do you notice?

Quick Practice

Problem 1: Find circumference when diameter = 10 units Problem 2: Find area when radius = 5 units Work these out and be ready to share!

Remember This!

Circumference = 2πr or πd (distance AROUND) Area = πr² (space INSIDE) π ≈ 3.14 (but leave as π for exact answers)