Mathematics, Geometry

Grade 5- 8

### Objective

Students are introduced to some basic concepts of geometry.

### Directions

Introduce students to the properties of triangles. The definition of a triangle is a figure with three sides, three angles, and three points. Triangles can be named by using three points in their correct sequence. For example, triangle ABC is a triangle with line segments drawn from A to B, B to C, and C to A. Note the rule that the three points cannot be on the same line.

The angles in a triangle are measured by degrees. A right angle measures 90 degrees. Any angle less than a right angle is an acute angle. Any angle greater than a right angle and less than a straight angle is called an obtuse angle. An angle that is more than 180 degrees and less than 270 degrees is called an oblique angle. This angle is not often used.

Triangles are named by the types of angles and sides they contain:

An equilateral triangle has three sides of equal length and three angles of equal measure.

An isocoles triangle has at least two sides with the same measure.

A scalene triangle has no equal sides.

A right triangle has one right angle (90 degrees).

An acute triangle has all angles less than 90 degrees.

An obtuse triangle has one angle greater than 90 degrees.

Have students use the first Triangle Puzzler activity sheet to identify different types of triangles. They can use their knowledge to solve the puzzler on the second activity sheet.

### Resources

- Triangle Puzzler activity sheets (2)