Acute Triangle – Definition with Examples
Created on Dec 23, 2023
Updated on January 13, 2024
Welcome to Brighterly, where we make math exciting and engaging for children of all ages! In this article, we will delve into the captivating realm of acute triangles, a fundamental concept in geometry. Triangles, as simple as they may seem, possess unique properties and types, which play a crucial role in solving a wide range of mathematical problems. So, grab your thinking caps and embark on an illuminating journey with us through the world of acute triangles, only at Brighterly!
What is an Acute Triangle?
An acute triangle is a special type of triangle in which all three interior angles are less than 90 degrees. In other words, all three angles are “acute,” hence the name acute triangle. These triangles can come in various shapes and sizes, but they all share this one common property: all their angles are less than 90 degrees.
Types of Acute Triangles
Acute triangles can be further classified based on the length of their sides. There are three main types of acute triangles:
 Equilateral acute triangle: All three sides of the triangle are of equal length, and all three angles measure 60 degrees.
 Isosceles acute triangle: Two sides of the triangle are of equal length, and the two angles opposite these equal sides are also equal.
 Scalene acute triangle: All three sides of the triangle are of different lengths, and all three angles have different measures.
What are the Different Types of Acute Triangles?
Now that you know the main types of acute triangles, let’s dig deeper into some more specific classifications. Acute triangles can also be categorized by their side lengths and angle measures. Some examples include:
 Obtuseangled isosceles triangle: This triangle has one obtuse angle (greater than 90 degrees) and two equal sides.
 Rightangled isosceles triangle: This triangle has one right angle (90 degrees) and two equal sides.
You can find more information on these types of triangles and others by visiting the Types of Triangles page on Brighterly.
Properties of Acute Triangle
Acute triangles have some unique properties that differentiate them from other types of triangles. Some of these properties include:
 All angles are less than 90 degrees.
 The sum of the angles in an acute triangle is always 180 degrees.
 An acute triangle can be equilateral, isosceles, or scalene.
 The shortest side is always opposite the smallest angle, and the longest side is always opposite the largest angle.
Acute Triangle Formulas
There are several formulas that can be used to find various properties of acute triangles, such as side lengths, angle measures, and area. Some common acute triangle formulas include:
 Law of Cosines: a² = b² + c² – 2bc * cos(A)
 Law of Sines: a/sin(A) = b/sin(B) = c/sin(C)
 Heron’s Formula for Area: Area = √(s * (s – a) * (s – b) * (s – c)), where s = (a + b + c) / 2 (semiperimeter)
The Perimeter of An Acute Triangle
The perimeter of an acute triangle is the sum of the lengths of its three sides. To find the perimeter, simply add up the side lengths:
Perimeter = a + b + c
Area of An Acute Triangle
The area of an acute triangle can be found using various methods, including the baseheight formula and Heron’s formula, as mentioned above. For example, if you know the base and height of an acute triangle, you can use the following formula to find its area:
Area = (base * height) / 2
If you don’t know the base and height, but know the side lengths, you can use Heron’s formula:
Area = √(s * (s – a) * (s – b) * (s – c))
where s is the semiperimeter, calculated as (a + b + c) / 2.
Solved Examples on Acute Triangle
Let’s take a look at some examples to better understand acute triangles and their properties.
Example 1: Find the area and perimeter of an acute triangle with side lengths 5, 12, and 13.
Solution:
First, let’s find the perimeter:
Perimeter = a + b + c = 5 + 12 + 13 = 30
Now, let’s find the area using Heron’s formula:
Semiperimeter (s) = (a + b + c) / 2 = (5 + 12 + 13) / 2 = 15 Area = √(s * (s – a) * (s – b) * (s – c)) = √(15 * (15 – 5) * (15 – 12) * (15 – 13)) = √(15 * 10 * 3 * 2) = 30
So, the area of the triangle is 30 square units, and the perimeter is 30 units.
Practice Problems on Acute Triangle
Here are some practice problems to help you apply what you’ve learned about acute triangles:
 Find the area of an acute triangle with side lengths 7, 24, and 25.
 If an acute triangle has side lengths 8, 15, and 17, what is its perimeter?
 In an isosceles acute triangle, two sides measure 10 units each, and the third side measures 8 units. Find the area of the triangle.
Conclusion
Acute triangles, despite their simplicity, open up a world of fascinating properties and applications in the field of geometry. By mastering the concepts of acute triangles and their related formulas, you are equipping yourself with valuable skills that will help you tackle various mathematical problems and enhance your overall understanding of geometry. But remember, the key to success lies in constant practice and exploration! So, continue to immerse yourself in the intriguing world of triangles, and before you know it, you’ll become a true geometry wizard, all thanks to Brighterly!
Frequently Asked Questions on Acute Triangle
What is an acute triangle?
An acute triangle is a special type of triangle where all three interior angles measure less than 90 degrees. These triangles can come in different shapes and sizes, but they all share this common property. Acute triangles are important in geometry and help us understand various properties and relationships among angles and sides.
How do I find the area of an acute triangle?
To find the area of an acute triangle, you can use either the baseheight formula or Heron’s formula, depending on the information available. The baseheight formula is: Area = (base * height) / 2. This formula requires the knowledge of the base and the corresponding height of the triangle. If you know the side lengths (a, b, and c) but not the height, you can use Heron’s formula: Area = √(s * (s – a) * (s – b) * (s – c)), where s is the semiperimeter, calculated as (a + b + c) / 2. Heron’s formula allows you to calculate the area of an acute triangle without knowing its height.
What are the types of acute triangles?
Acute triangles can be classified into three main types based on the length of their sides:

Equilateral acute triangle: In this type of acute triangle, all three sides are of equal length, and all three angles measure 60 degrees. Equilateral triangles are always acute.

Isosceles acute triangle: An isosceles acute triangle has two sides of equal length, and the two angles opposite these equal sides are also equal. The third side is of a different length, and the third angle is also different. These triangles can have varying shapes, but they all share the property of having two equal sides and two equal angles.

Scalene acute triangle: In a scalene acute triangle, all three sides are of different lengths, and all three angles have different measures. These triangles can have various shapes, but they all have the property of having no equal sides or angles. Scalene triangles can be acute, right, or obtuse, depending on their angle measures.
Understanding the different types of acute triangles helps us recognize their unique properties and solve various mathematical problems related to triangles.