Definition: A triangle is a polygon with 3 sides. Types of triangles by sides Definitions Directions for interactivity
Directions: In the interactivity, click and drag the sliders for side length and notice
Click and drag slider zoom to zoom in or out (and get similar triangles!).
Click and drag point А to move and point В to rotate.

Rule: The sum of the inside angles of a triangle is 180°. Types of triangles by angles Definitions Directions for interactivity
Directions: In the interactivity, click and drag the angle sliders \alpha and \beta and notice
Click and drag slider zoom to zoom in or out (and get similar triangles!).
Click and drag point А to move and point В to rotate.
Get the latest Java Plugin here. 
Formulas for perimeter and area 
Related themes:
 Right Triangle
 Congruency, Congruent Triangles
 Similarity, Similar Triangles
 Heron's Formula
 Polygon
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