Shapes can be classified and sorted according to observable geometric attributes, such as the number and length of sides, number of vertices, presence of right angles, and whether they are two-dimensional or three-dimensional. A shape may belong to more than one category, and its classification does not change when it is rotated, resized, or drawn in an unfamiliar orientation; this reasoning supports precise definitions and hierarchical classification in later geometry.
Look at each shape’s attributes, or features. Count its sides and vertices, and check for right angles. Do not decide by how the shape is turned or sized.
Example: Sort these shape cards into groups:
Use these groups:
Step 1: Check Card A.
A triangle has sides, so it does not have four sides. Put it in Group 3.
Step 2: Check Card B.
Even though the square is turned, it still has sides and right angles. Put it in Group 1.
Step 3: Check Card C.
A rectangle has sides and right angles. Put it in Group 1.
Step 4: Check Card D.
This shape has sides, but its corners are not right angles. Put it in Group 2.
Sorted groups:
A shape can fit more than one description. For example, a square has four sides and four right angles. Turning, resizing, or drawing a shape in a new way does not change its attributes.
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