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| +, - | Math |
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| More Math | Triangles | More Shapes |
A triangle is a three-sided figure. The sum of the interior angles of a triangle is 180 degrees. Each of the three points on the tips of a triangle is called a vertex (the plural of vertex is vertices).
The perimeter of a triangle is the sum of the lengths of the three sides. The area of a triangle is (1/2)*base*height.
Triangles can be classified by the length of their side or by their interior angles.
Classifying triangles by side length:
 equilateral triangle The sides of an equilateral triangle are all the same length and all the interior angles are 60 degrees. |
 isosceles triangle An isosceles triangle has two sides that are the same length and two interior angles that are the same. |
 scalene triangle The sides of a scalene triangle are all different lengths. A right triangle can be a scalene triangle (but not all right triangles are scalene triangles). |
The interior angles of a all triangles add up to 180 degrees. Every triangle has at least two acute angles (an acute angle is less than 90 degrees).
Classifying triangles by interior angles:
 acute triangle All three interior angles of an acute triangle are acute (less than 90 degrees). Equilateral triangles are acute triangles. |
 obtuse triangle One of the interior angles of an obtuse triangle is obtuse ( an obtuse angle is over 90 degrees). |
 right triangle A right triangle has one angle that is a right angle (a right angle is a 90-degree angle). The Pythagorean theorem states that for a right triangle, the sum of the squares of the two shorter sides is equal to the square of the hypotenuse (h): a2 + b2 = h2. The hypotenuse is the longest side of a right triangle, and is the side opposite the right angle. |
Triangle Worksheets:
 Triangle Worksheet Read about triangles, do dot-to-dots, draw them, color them, and write the names of things with a triangular shape. Or go to the answers. |
 Triangle Classification Worksheet Read about how to classify triangles with respect to side length and interior angles (equilateral, isosceles, scalene, right, acute, and obtuse triangles). Or go to the answers. |
 Angles and Triangles Label the angles (acute, right, obtuse, and straight) and triangles (equilateral, isosceles, scalene, and right). Answers |
Books to Print
 Things Shaped Like Triangles A Printable Activity Book A small, triangular shaped book with triangular things to draw, including mountain, volcano, rocket, banner, and pyramid. A one-page printout. |
 Triangles A Printable Activity Book A small, triangular shaped book about triangles, with pages: circle the triangles, draw a triangle, definition of an equilateral triangle, definition of an isosceles triangle, and definition of a right triangle. A one-page printout. |
| +, - | Math |
x, ÷ |
| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
| Counting | Addition | Subtraction | Multiplication | Division |
| Number Line | Fractions | Decimals | Rounding | Graphs |
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