How to Classify Triangles Based on Sides and Angles

Classify Triangles Based on Sides and Angles

VIDEO DESCRIPTION

TenMarks teaches you how to classify triangles based on sides and angles.

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VIDEO TRANSCRIPT

In the lesson, let’s learn about classifying triangles, and the problem wants us to classify each of the triangles below according to its sides and considering the angles. Let’s do them one by one.

If we look at the first triangle, the triangle has got three sides and we can visually observe that none of the sides are congruent. What that means is that all sides are of different lengths. As we can see, this is the longest side, this is the second longest side and this is the shortest side. So none of the sides are congruent, that means it is the scalene triangle. That’s the first point that we know.

The second is we can see that all angles are different, and one of the angles is above 90 degrees or greater than 90 degrees, this angle is an obtuse angle. So if we know that it’s a scale in triangle with the definition of angles being obtuse. So when I look at the angles, it’s an obtuse angle triangle, and when I look at the sides, it’s scalene. So the definition or the classification of this is a scalene obtuse triangle. That’s the first one.

Second one is looking at part B. In part B, we can see that by the nature of these marks, two sides are congruent. Since two sides are congruent, we know that this is an isosceles triangle. So from a sides perspective, it is an isosceles triangle. From an angle perspective I can see it’s got a right angle, so it is also a right angle triangle, which means that the classification of this would be an isosceles right triangle.

When we look at the third one, we can see that it's a right triangle. So the angle is easier to spot. This is correct. And we can see that all three sides are different, no congruent sides, which means it is a scalene right triangle.

Fourth, we can see the two sides are congruent and this angle is an obtuse angle. So this is an isosceles triangle and we know it’s an obtuse triangle, so isosceles obtuse triangle.

Key to remember here is to look at the classification of sides first. If the sides are congruent, two sides are congruent, it’s isosceles. If three are congruent, it is called equilateral. If no sides are congruent, then it’s scalene. Second, we look at the classification of the angle. If the angle is right, then it’s a right triangle. If the angle is obtuse, then it’s an obtuse triangle. You get the idea.