### As a geometry student, you have been told about angle relationships, but maybe you haven't grasped the concept behind complementary angles, or supplementary angles. What is a linear pair? What is special and different in a linear pair from just supplementary angles?

### In this lesson, we approach the teaching of these concepts making use of the GeoLegs. GeoLegs enable to show in a very concrete way the abstract idea behind those definitions. If you don't have GeoLegs to practice with, it doesn't matter; we provide you of high quality pictures and animations that accomplish the same goal. As in other lessons in the geometry section, and after most of the examples; you will be presented with some suggested problems to solve. For that you will interact on the screen with your stylus and the marker tools menu.

** Lesson's Content **

** Lesson's Glossary **

**Angle **

Geometric shape formed by two rays (initial and ending sides of the angle) that share a common endpoint called the vertex. You may name an angle using the vertex, or a point in each ray and the vertex label in the center.

**Acute angle **

An angle that is between 0 and 90 degrees.

** Complement **

Angle that together with the given angle adds up to 90 degrees.

** Complementary angles **

Two angles whose measures, when added together, equal 90 degrees.

** Obtuse angle **

An angle whose measure is greater than 90 but less than 180 degrees.

** Supplement **

Angle that together with the given angle adds up to 180 degrees.

**Supplementary angles **

Two angles whose measures, when added together, equal 180 degrees.

**Vertical angles **

Nonadjacent angles that are opposite by the vertex and are formed by two intersecting straight lines.

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