Triangles - Area of a Triangle
Welcome to Quatr.us Study Guides!

Triangles

Triangle

A triangle is any set of three points on a plane and the lines connecting those points to each other, as long as the three points aren't all on the same line (that would just be a line). Or, you could think of a triangle as the part of the plane that lies inside those line segments. A triangle is flat - it has no thickness. But every triangle has a perimeter and an area, and three angles.

Triangle

The three angles of a triangle will always add up to 180 degrees, no matter how big or how small the triangle is. Think of it this way: a rectangle has four 90 degree angles, or right angles. Adding those four 90 degree angles together shows us that a rectangle has 360 degrees. But a triangle is half of a rectangle, split from corner to corner. So it has to have half the degrees of a rectangle, or 180 degrees. Because of this, if you know the measurements of two angles of a triangle, you can always figure out how big the third angle is by adding the two known angles together and subtracting that from 180 degrees.

Some kinds of triangles are more useful in math than others, and they have their own names. An equilateral triangle has all three sides the same length, like the green triangle at the top of this page. An isoceles triangle has two sides the same length (so all equilateral triangles are also isoceles triangles). And a right triangle has one angle that is exactly 90 degrees (a right angle), so the other two angles together add up to 90 degrees.

If you move a triangle through space, you'll get a solid object called a triangular prism. A pyramid, on the other hand, you make by leaning triangles against each other.

Isoceles Triangles
Equilateral Triangles
More about Geometry

Bibliography and further reading about geometry:

More about Geometry
More Easy Math
Quatr.us home


Please help other teachers and students find us: link to this page from your class page.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram, Pinterest, or Twitter, or buy her book, Vandals to Visigoths.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter, or buy her book, Vandals to Visigoths.
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Check out our new ebook: Short and Simple: Ancient Greek Myths! - just out! Twenty-five easy to read, illustrated stories, from Pandora to Medea, Icarus, and the Trojan Horse (you can read these online as samples). Get it this week for just $14.99, five dollars off the regular price of $19.99.
Cite this page
  • Author: K.E. Carr
  • Title:
  • Site Name: Quatr.us Study Guides
  • Publisher: Quatr.us
  • Date Published:
Did you find what you needed? Ask your teacher to link to this page so other people can use it too! Send it in and win a Quatr.us "Great Page!" award!
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Comment on This Article
Quatr.us is loading comments...
(Comments will appear after moderation, if they are kind and helpful. Feel free to ask questions, and we'll try to answer them.)
Cite this page
  • Carr, K.E. . Quatr.us Study Guides, . Web. 27 July, 2017
ADVERTISEMENT