The triangle inequality says a detour is never shorter than going straight. ‖u + v‖ ≤ ‖u‖ + ‖v‖ Equality holds exactly when u and v are parallel and point the same way; in the general case the direct vector u + v is strictly shorter than following u then v. The same statement reappears for real numbers as |a + b| ≤ |a| + |b| and for integrals as |∫f| ≤ ∫|f|, with the reverse form ‖u‖ − ‖v‖ ≤ ‖u − v‖ often the more useful of the two. This single inequality is what makes a distance a distance.
Triangle Inequality: Discovery Lesson

Prove Reverse Triangle Inequality
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Triangle Inequality Theorem Discovery Activity 7.G.A.2


Inequality In A Triangle
Triangle Inequality Theorem - fun with licorice - geometry activity


Get students real world practice with the triangle inequality theorem with these 11 activity ideas. Includes print and go resources, discovery learning, online math tools, challenge questions, and more. Check it out!
Triangle Inequality Of Norms
Free Triangle Inequality Theorem foldable for Geometry Classroom
Triangle inequality theorem










Students will explore the triangle inequality theorem by trying to create their own triangles with various side lengths. Students will cut out strips of paper to represent the side lengths of the triangles, then will put a given three together to test and see if a triangle can be formed.
Triangles are among the most fundamental shapes in geometry, and their properties help us understand countless mathematical and real-world concepts. One of the most important properties of triangles is expressed through the Triangle Inequality Theorem — a principle that determines whether three given line segments can form a triangle.