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Mathematics · Glossary

What is Special triangles?

Also known as: isosceles triangle · equilateral triangle · right triangle

Definition 41.1 Primary & Middle School Mathematics · Chapter 41 — Triangles and Quadrilaterals

A triangle ABCABC has three vertices and three sides. It is:

  • isosceles at AA when AB=ACAB = AC (two equal sides);
  • equilateral when AB=BC=CAAB = BC = CA (three equal sides);
  • right-angled at AA when the angle BAC^\widehat{BAC} is a right angle. The side [BC][BC] opposite the right angle is called the hypotenuse.
The three special triangles. Small tick marks indicate equal sides; the square marks the right angle.
The three special triangles. Small tick marks indicate equal sides; the square marks the right angle.
Constructing a triangle with the compass: the vertex C is the crossing point of two arcs. (In you will see when such a construction is possible.)
Constructing a triangle with the compass: the vertex CC is the crossing point of two arcs. (In Chapter 51 you will see when such a construction is possible.)
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