Geometry Learning Tool

Triangle Learning Tool

Drag the A, B, and C vertices to discover how side lengths, angles, and triangle names all fit together.

Explore triangle types, angle sum, perimeter, and area in one live diagram.

Big idea: every true triangle has three interior angles that add to 180 degrees. Move any corner and the other measurements update instantly.

Interactive triangle explorer

Drag a vertex in the diagram or use a preset. The side lengths, angle measures, classifications, and explanation all update together.

Draggable triangle diagram Triangle with draggable vertices A, B, and C plus live side and angle labels. A B C AB 46.2 units BC 34.7 units CA 42.6 units Scalene triangle Angles: 45.7 + 61.7 + 72.5 = 180 Acute by angles A B C
Drag tip: move A, B, or C. The current triangle is scalene by sides and acute by angles.
Angle A45.7 degrees
Angle B61.7 degrees
Angle C72.5 degrees
A = 45.7 + B = 61.7 + C = 72.5 = 180 degrees

The colored bar is a straight angle split into the triangle's three interior angles.

Side AB46.2 units
Side BC34.7 units
Side CA42.6 units
Side type: Scalene Angle type: Acute Largest angle: C (72.5 degrees)

How to use this tool

Choose a preset to see a special triangle, or drag A, B, or C to make your own.

  • Clicked presets turn yellow, such as the Equilateral button.
  • Dragging any vertex clears the preset highlight because the triangle is now custom.
Side-based presetsShape
Angle-based presetsAngles
Side classificationScalene
Angle classificationAcute
Perimeter123.5 units
Area705 square units

What is happening?

All three side lengths are different, so the triangle is scalene. Its angles are usually all different as well. It is acute because every angle is smaller than 90 degrees. The largest angle is C, and it sits across from the longest side.

Current definition

A scalene triangle has no equal sides.

What students should remember

Sides name the triangle

Equilateral means three equal sides, isosceles means two equal sides, and scalene means no equal sides.

Angles reveal the behavior

Acute triangles have all angles below 90 degrees, right triangles have one 90 degree angle, and obtuse triangles have one angle above 90 degrees.

The sum stays fixed

Dragging changes the individual angles, but a valid triangle always keeps A + B + C equal to 180 degrees.