PAIBOTLearn
Sign inSign up

Isosceles & equilateral triangles

Basic shapes

Japanese school year: Elementary 3

What you learn

Learn the properties of isosceles and equilateral triangles regarding their side lengths, angles, and compass construction. These geometric features are widely utilized in architectural trusses and structural design. Having prior knowledge of basic triangle definitions and length measurement will help you understand and draw these figures with ease.

Go to practice

Key points

This formula shows a feature of an isosceles triangle. When two sides a and b are equal, the bottom angles B and C are also equal.

∠B=∠C(a=b)\angle B = \angle C \quad (a = b)

This equation defines an equilateral triangle. A triangle where all three sides a, b, and c are equal is an equilateral triangle.

a=b=ca = b = c

This equation shows the angles of an equilateral triangle. All three angles A, B, and C are equal, each measuring 60°.

∠A=∠B=∠C=60∘\angle A = \angle B = \angle C = 60^\circ

This formula finds the perimeter L of an equilateral triangle. Since all sides have length a, multiply the side length by 3.

L=3a(a=b=c)L = 3a \quad (a = b = c)

Choose a set to practice.