types of triangles

A triangle has three sides and three angles
		The three angles always add to 180°

Equilateral, Isosceles and Scalene

There are three special names given to triangles that tell how many sides (or angles) are equal.

There can be 3, 2 or no equal sides/angles:

	Equilateral Triangle Three equal sides Three equal angles, always 60°
	Isosceles Triangle Two equal sides Two equal angles
	Scalene Triangle No equal sides No equal angles

What Type of Angle?

Triangles can also have names that tell you what type of angle is inside:

	Acute Triangle All angles are less than 90°
	Right Triangle Has a right angle (90°)
	Obtuse Triangle Has an angle more than 90°

Combining the Names

Sometimes a triangle will have two names, for example:

Right Isosceles Triangle Has a right angle (90°), and also two equal angles Can you guess what the equal angles are?

Play With It ...

Try dragging the points around and make different triangles:

You might also like to play with the Interactive Triangle.

Perimeter

The perimeter is the distance around the edge of the triangle: just add up the three sides:

Area

The area is half of the base times height.

• "b" is the distance along the base
• "h" is the height (measured at right angles to the base)

Area = ½ × b × h

The formula works for all triangles.

Note: a simpler way of writing the formula is bh/2