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Obtuse Triangle – Definition, Examples | EDU.COMEDU.COMResourcesBlogGuidePodcastPlanBackHomesvg]:size-3.5">Math Glossarysvg]:size-3.5">Obtuse TriangleObtuse Triangle – Definition, ExamplesTable of ContentsObtuse Triangles Definition of Obtuse Triangles

An obtuse-angled triangle is a triangle in which one of the interior angles measures more than 90° degrees. In an obtuse triangle, if one angle measures more than 90°, then the sum of the remaining two angles is less than 90°. All the angles of the triangle still add up to 180 degrees. The side opposite the obtuse angle in the triangle is the longest.

Obtuse triangles can be classified into two types based on their sides. An isosceles obtuse triangle has two sides of equal length. A scalene obtuse triangle has all sides of unequal length. It's important to note that an equilateral triangle can never be obtuse since all angles in an equilateral triangle measure 60°. Additionally, a triangle cannot be both right-angled and obtuse-angled at the same time.

Examples of Obtuse Triangles Example 1: Identifying an Obtuse Triangle Problem:

Is the following picture an example of an obtuse triangle?

Triangle

Step-by-step solution:

Step 1, Look at all three angles in the triangle to see if any one of them is greater than 90°.

Step 2, Check each angle carefully. We can see that all the angles in this triangle are less than 90°.

Step 3, Make a conclusion based on our observation. No, the given figure is not an obtuse triangle as all the angles are less than 90°.

Example 2: Checking Angles for an Obtuse Triangle Problem:

Will the following set of angles form an obtuse triangle? 95°, 30°, 55°.

Step-by-step solution:

Step 1, Check if any angle is greater than 90°. We can see that 95° is greater than 90°, so it is an obtuse angle.

Step 2, Check if the sum of all three angles equals 180°. We add: 95°+30°+55°=180°95° + 30° + 55° = 180°95°+30°+55°=180°

Step 3, Make our conclusion. Yes, these angles will form an obtuse-angled triangle, as 95 degrees is an obtuse angle and the sum of the angles is 180 degrees.

Example 3: Identifying Types of Obtuse Triangles Problem:

What type of obtuse triangle is shown in the figure?

Triangle

Step-by-step solution:

Step 1, Check if the triangle has an obtuse angle. We can see one angle is clearly greater than 90°.

Step 2, Look at the sides of the triangle. Are any sides equal in length?

Step 3, We can see that none of the sides are equal in length.

Step 4, Make our conclusion based on what we learned about triangle types. It is an obtuse scalene triangle as none of its sides are equal.

Comments(6)CCoachNickNovember 4, 2025This obtuse triangle def. was a lifesaver! Helped my students grasp the concept easily. Clear examples made it super simple. Thanks!

MCMs. CarterSeptember 17, 2025I used this obtuse triangle definition and examples to help my kids with their homework, and it made everything so clear! The step-by-step solutions are super helpful for understanding tricky concepts.

MCMs. CarterSeptember 10, 2025I’ve used the obtuse triangle definition and examples on EDU.COM to help my kids with their homework. The clear explanations and step-by-step solutions really made it easy for them to understand. Great resource!

MCMs. CarterAugust 27, 2025I’ve been using this page to help my kids with their homework, and the clear examples of obtuse triangles made it super easy for them to understand. Love the step-by-step approach!

NNatureLover82August 20, 2025I’ve been helping my kid with geometry, and this page made obtuse triangles so easy to understand! The examples were spot-on, and now he’s confident identifying them in his homework. Great resource!

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