## Definition

An obtuse triangle is a figure where one of the three angles measures more than 90°, and the other two angles measure less than 90°.

## Properties

1. One of the three interior angles
measures more than 90°, and two others are acute angles; in ∆ABC, ∠ABC is the obtuse
angle

2. The sum of the two acute angles is always less than the obtuse angle,

so ∠BAC + ∠ACB < ∠ABC

3. The side opposite the obtuse angle
is the longest side of the triangle, so AC is the longest side

## Types

Obtuse triangles are classified into two types: 1) obtuse scalene triangle, and 2) obtuse isosceles triangles.

The differences between the types are given below:

## Formulas

**Area (****A****) = ½ (****b**** × ****h****)**,** **where *b* = base and *h* = height

**Perimeter (****P****) = ****a**** + ****b**** + ***c**,* where *a*, *b*, *c *are the measures of three sides