What this lesson shows
A compass opened to 3 centimeters draws a circle. From the center to the edge is the radius, 3 cm. Edge to edge through the center is the diameter, 6 cm, twice the radius.
The worked example
The lesson works this one step by step: a circle, radius 3 cm. Then your kid tries one like it on paper.
The steps
- Center: where the compass point sits
- Radius: center to the circle
- Diameter: edge to edge through the center
- Diameter = 2 × radius
- Radius = diameter ÷ 2
Helping at home
Open a compass along a ruler to the radius, keep the point still, and turn the pencil around. The point is the center. The diameter goes edge to edge through the center: twice the radius. The radius is half the diameter.
If your kid gets stuck
Is the diameter one radius or two?
Watch it with Lux
With Lux, this lesson is a narrated video and a printed page your kid works on. Then Lux helps with the same math on their own worksheet, one question at a time.
More in this unit
- Triangles two ways
- Every name that fits
- Not only the last name
- Solid figures
- Turning does not change it
- Volume by packing cubes
- No gaps, no overlaps
- Volume by formula
- The base is an area
- Find the missing edge
- Two boxes put together
- Nets of solids
- Area of parallelograms and triangles
- The angles of a triangle
- Area of a trapezoid
- Estimating around a curve
- Perimeter, area, or volume?
- Surface area with a net