Parts of a Circle

In the same circle the diameter is twice the radius: d = 2r

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About This Practice

Three essentials of a circle: the center fixes its position, the radius fixes its size, and the diameter is twice the radius (d = 2r). Grow and shrink the radius to watch the circle change, and switch between radius and diameter views to see that all radii in one circle are equal — and all diameters too.

Grow and shrink the radius and watch the circle change; switch between radius and diameter views to see that all radii are equal and d = 2r.

EasyEstimated Time: 8mincenterradiusdiameterd=2r

How to Play

  1. Find the center: the point in the middle.
  2. Meet the radius: the segment from center to edge — grow and shrink it to resize the circle.
  3. Meet the diameter: the segment through the center with both ends on the circle.
  4. Compare: which is twice which, diameter or radius?
  5. Try another radius and check that d = 2r always holds.

Learning Objectives

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