Identify triangles

A triangle is a closed, two-dimensional polygon with exactly three straight sides, three vertices, and three angles; its sides may differ in length, and its orientation, size, or appearance does not change its identity. Identifying triangles involves attending to these defining properties rather than relying on a familiar visual prototype, while distinguishing them from open shapes, curved boundaries, and polygons with other numbers of sides.

Detailed Explanation: Identify triangles

To identify a triangle, check its boundary:

It is closed—the sides connect all the way around.
It has exactly 3 straight sides.
It has exactly 3 vertices (corners).
It has exactly 3 angles.

The triangle can be large, small, tilted, or have sides of different lengths.

Example

Is this shape a triangle?

        A
       / \
      /   \
     B-----C

Step 1: Check that it is closed.
The sides connect from $A$ to $B$ , from $B$ to $C$ , and from $C$ back to $A$ . There is no gap.

Step 2: Count the straight sides.
The shape has 3 straight sides: $\overline{AB}$ , $\overline{BC}$ , and $\overline{CA}$ .

Step 3: Count the vertices.
The corners are $A$ , $B$ , and $C$ , so there are 3 vertices.

Conclusion:
Yes, the shape is a triangle because it is closed and has exactly 3 straight sides, 3 vertices, and 3 angles.

Learn by doing: Identify triangles

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Shapes - 2D Simple (Real World)

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Identify triangles

Detailed Explanation: Identify triangles

Learn by doing: Identify triangles

Practice with unlimited practice problems

Practice:

Shapes - 2D Simple (Real World)