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K6 Math Logo
K6 Math Logo

Master the Obtuse Triangle with these Seven Specific stages.

The Obtuse Triangle is identified by angles.
An Obtuse triangle wil ALWAYS have one angle which is Obtuse. This is an angle that measures between 90 and 180 degrees. So if a triangle has an angle measuring >90 degrees and <180 degrees, it is considered to be Obtuse.
At this stage of geometry your child should easily be able to distinguish the relationship between angles. They should be able to identify Right Angles, Straight Angles, Obtuse Angles and Acute Angles.
If they are weak in this skill, I highly recomend offereing them some basic geometry angles worksheets to bring them up to speed before continuing.

The seven steps detailed bellow take you from basic identification all the way through to taking a detailed look at the theorems involving the scalene triangle. These steps also include 'pit stops' to complete fun geometry projects and coloring sheets.

These are nice 'breathers' on the learning curve, but they are excellent ways of reinforcing the new knowledge in ways that your kid can get a real life, hands on approach to understanding the basic geometry concepts included.

Okay, so let's get started ...
identify triangles


How do we know a triangle is an Obtuse Triangle?

An Obtuse trinagle is simply identified by its angles. If one angle is greater than 90 degrees and less than 180 degrees (ie Obtuse) then the triangle itslef is an Obtuse Triangle, and that's it!
Having the skill to identify these triangles, rests solely, with the ability to identify different types of angles. Make sure your child is comfortable with this.
identify a scalene trinagle

Calculate Area and Perimeter

How to calculate the Area and Perimeter of an Obtuse Triangle?

The Area of a this type of triangle is calculated the same way as EVERY triangle. It is always half the length of the base multiplied by the perpendicular height of the triangle, in this case, the perpendicular height is always the length of the vertical side of the triangle.
Ther Perimeter of ANY shape is simply the sum total of all the lengths of the shape - and a triangle is no different.
The perimeter of this shape is a + b + h

Kindergarten math

How to construct an Obtuse Triangle

To complete this, you will need a ruler, pencil, protractor and a blank piece of paper!

Step 1 Draw a straight line and indicate one point where you would like to have a vertex of your triangle.
Step 2 Ensuring proper placement of your protractor, chose any number of degrees between 90 degrees and 180 degrees, and create your second point. If you are given a specific angle, use this.
Step 3Draw a light construction line between these two points. You now have a line where the second point of your triangle can exist. Anywhere on this line. If however in directions, if you are given specific line lengths, you now measure along this line, to find your second vertex.
Step 4Again, if you are given specific line lengths, measure to find your third vertex. If not, you can simply connect your two exisiting lines again, to create your third and final vertex and side.
Step 5 Redraw your obtuse triangle connecting your three vertices in a harder stroke to give it more definition.

Download one ttrinagle worksheet, or all of them, to offer your student the practice they need to identify these shapes.
Kindergarten math

Relationship to 3D Shapes

The 3d Figures a Kindergarten through sixth grade student is most likely to deal with, created by this triangle will either be a Triangular Prism or pyramid.
Kindergarten math

Geometric Coloring Sheets

The use of coloring sheets allows your child to start experimenting with triangles. A great first step is to encourage your child to color in triangles adjacent to eachoter with the same color, until their shape starts to look like 'something'. Perhaps that something will be a rectangle or a house. By doing this, your child will start to realize the connection between different shapes. You will find some nice free geometric coloring pages to download here.
identify obtuse triangle

Fun Geometry Projects


geometry theorems

Theorems & Proofs


I have created Free printable triangle worksheets for you to offer your child for more practice. Download, print and give them to your kids!

Return from this Obtuse Triangle page to our Diffferent Types of Triangles Section.
Return from this page to K6 Geometric Shapes Home Page, to explore all the other great sections I have to offer.

If you have any suggestions on how to make this site better for you and other readers, please don't hesitate to contact me. I love to hear from my readers, and with a little feedback, I can make this a great resource for parents, teachers and tutors alike.

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