What is a Triangle:

A polygon with 3 edges,
3 vertices, 3 angles.
We take 3 points and connect them with 3 sides below denoted as ΔPQR:

Properties of a Triangle:

Sum of the three interior angles = 180°
Sum of the 2 sides > 3rd side
A triangle with vertices (points) P, Q, R:
is denoted as ΔPQR

Area of a Triangle

With base b and height h:
A = 1/2bh

Acute Triangle:

All 3 angles measure less than 90°

Right Triangle:

Has one angle measuring 90° (right)
The other two angles < 90°

Obtuse Triangle:

Has only one angle measuring > 90°
Obtuse angle is opposite the long side

Scalene Triangle

No Sides Are Equal

Isosceles Triangle

2 sides Are Equal

Equilateral Triangle

All 3 sides are equal

How does the Triangles Calculator work?

This lesson walks you through the basics of a triangle and shows you triangle types like acute, right, obtuse, scalene, isosceles, equilateral.

What 2 formulas are used for the Triangles Calculator?

  1. Triangle PQR is written as ΔPQR
  2. The sum of the three interior angles of a triangle equals 180°

For more math formulas, check out our Formula Dossier

What 7 concepts are covered in the Triangles Calculator?

acute triangle
A triangle for which all interior angles are acute.
equilateral triangle
A triangle with 3 equal sides
isosceles triangle
A triangle with two equal sides and an unequal third side
obtuse triangle
A triangle which has an obtuse angle as one of its interior angles.
right triangle
triangle in which one angle is a right angle
scalene triangle
a triangle with three unequal sides
a flat geometric figure that has three sides and three angles

Triangles Calculator Video


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