Know the formulas for the area and circumference of a circle and use them to solve problems; give an informal derivation of the relationship between the circumference and area of a circle.
In plain words: Students use the formulas for the circumference and area of a circle to solve problems, and see informally why the area formula follows from the circumference.
Quick picks
Example problem- Assign problem on Goblins →The radius of a circle is 2 units.
What is its circumference?
Use 3.14 for π. - Teach it with
A rope around the Earth7th grade · Circles · 2 min- Common mistake
- Mixing up the formulas: for r = 3, the circumference is 2π(3) ≈ 18.8 and the area is π(3²) ≈ 28.3, not the other way around.
Example Problems
The radius of a circle is 2 units.
What is its circumference?
Use 3.14 for π.
What is its circumference?
Use 3.14 for π.
The radius of a circle is .
What is the diameter of the circle?
What is the diameter of the circle?
The radius of a circle is . What is the diameter of the circle?
Khan Academy ResourcesArea of circles reviewCircumference reviewRadius, diameter, & circumferenceRadius and diameterArea of a circleCircumference of parts of circlesArea of parts of circlesArea and circumference of circles challengeCircumference and rotationsCircumference of a circleRadius, diameter, circumference & πArea of a circleLabeling parts of a circleImpact of increasing the radiusArea of a shaded regionRadius & diameter from circumferenceFinding circumference of a circle when given the area
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