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Identify circles

A circle is a two-dimensional, closed, round shape in which every point on the boundary is the same distance from a central point; it has no straight sides or vertices. Identification depends on these defining attributes rather than orientation, size, color, or whether the circle appears as part of a familiar object. This understanding supports later work with attributes of shapes, symmetry, length, and area.

Detailed Explanation: Identify circles

A circle is a closed, round shape. It has:

  • no straight sides,
  • no corners or vertices,
  • a boundary that is the same distance from the center all the way around.

Do not use color, size, or direction to decide. A large circle and a small circle are both circles.

Example: Which shape is a circle?

  • Shape A: ○
  • Shape B: △
  • Shape C: □
  • Shape D: an oval

Step 1: Check whether the shape is closed.
All four shapes are closed.

Step 2: Look for straight sides and corners.
Shapes B and C have straight sides and corners, so they are not circles.

Step 3: Compare the round shapes.
Shape D is stretched longer in one direction, so it is an oval. Shape A is round all the way around.

Answer: Shape A is a circle because it is closed, round, and has no straight sides or corners.

Learn by doing: Identify circles

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Shapes Reversed - 2D Complex


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