In geometry, the radius of a circle is a line segment that connects the center of the circle to any point on the circle. It is the distance from the center of the circle to any point on the circle's circumference. The radius is denoted by the letter "r".

- The radius is always half the diameter of a circle.
- All radii of a circle are congruent to each other.
- The radius is used to calculate the circumference and area of a circle.

The radius is an important parameter when calculating the properties of a circle. Here are the key formulas involving the radius:

C = 2 * π * r

Where C is the circumference and π is approximately 3.14.

A = π * r^{2}

Where A is the area of the circle.

- Practice calculating the circumference and area of circles using the radius.
- Draw circles and label the radius on each to visualize its properties.
- Work on problems involving finding the radius when given the circumference or area of a circle.
- Understand the relationship between the radius and diameter of a circle.

Study GuideDiameter of Circle Worksheet/Answer key

Diameter of Circle Worksheet/Answer key

Diameter of Circle Worksheet/Answer key

Diameter of Circle

Geometry (NCTM)

Use visualization, spatial reasoning, and geometric modeling to solve problems.

Use geometric models to represent and explain numerical and algebraic relationships.

Measurement (NCTM)

Apply appropriate techniques, tools, and formulas to determine measurements.

Select and apply techniques and tools to accurately find length, area, volume, and angle measures to appropriate levels of precision.

Develop and use formulas to determine the circumference of circles and the area of triangles, parallelograms, trapezoids, and circles and develop strategies to find the area of more-complex shapes.

Connections to the Grade 6 Focal Points (NCTM)

Measurement and Geometry: Problems that involve areas and volumes, calling on students to find areas or volumes from lengths or to find lengths from volumes or areas and lengths, are especially appropriate. These problems extend the students' work in grade 5 on area and volume and provide a context for applying new work with equations.