The first instance of Recognizing triangles is under the 4th grade (U.S.) Math Mission. This exercise practices the classification of triangles based on their angles and sides.

Types of Problems

There are three types of problems in this exercise:

  1. Select triangle types: This problem has a triangle and asks the user to use a multiple select all the correct classifications of the triangle.

    Select triangle types

  2. Select triangle descriptions: Similar to problem type one, but instead of selecting the formal property name, the user selects the descriptions that are accurate regarding the triangle.

    Select triangle descriptions

  3. Drag into category: This problem has four triangles on cards and users are supposed to drag each triangle into the appropriate category.

    Drag into category


This exercise is easy to get accuracy badges as long as user knows the basic triangle type definitions by angles and by sides. The speed badges are medium because of the time involved to select more than one answer and drag the cards.

  1. Khan Academy considers an equilateral triangle to be isosceles, that is, the definition of an isosceles triangle is having at least two congruent sides.
  2. On problem type one most triangles will have exactly two selections, the classification based on angles (acute, right, obtuse) and the classification based on sides (scalene, isosceles, equilateral).
  3. On the third problem type it is fast for dragging if user takes the triangles that fit in the lower category first. Otherwise the picture can scroll down making it difficult to reach the bottom category.

Real-life Applications

  1. Architects use triangles when building bridges, roofs on houses, and other structures.

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