The Right Triangle

The term Right Triangle is one of six means of identifying triangles your child must know.

It is also the easiest to start your triangle studies with.  It becomes very important when your child progresses to studying the circle and the cone.

Using this triangle to explain a triangle area is easiest.  Use the method of putting two triangles together to get a rectangle. Rectangles are one of the easier quadrilaterals to calculate the area of.  Because you put two triangles together to get the rectangle, the area of the triangle must be HALF!


  • A Right Angled Triangle always has a 90 degree angle.
  • It CAN be an Isosceles Triangle, giving us a Right Isosceles Triangle.
  • It CAN be a scalene Triangle, giving us a Right Scalene.
  • It CAN NEVER be an Equilateral Triangle.

What else is so important about a right Triangle?

Because we know the sum of all angles in any triangle is 180 degrees, this tells us that the sum of the two non right angles is also 90 degrees.

If you place your compass at the mid point of the line opposite the Right angle and construct a semi circle around the triangle, you will notice that the vertex which is the 90 degree angle will always be on the circle.  This is because ANY triangle containing the two points of the diameter of a circle and any other point on the circle will create a 90 degree angle.

Finding the length of the longest side of a right angled triangle (the Hypotenuse) is simplified with the formula: the square of the hypotenuse is the sum of the squares of the other two sides!)

For a site devoted entirely to Elementary Geometry please visit K6-Geometric-Shapes.com and don't forget to browse all that Printable Math Worksheets has to offer.

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