Angles

Objectives:

Name Angles  

Measure Angles

 

Protractor

Vocabulary:

Ray, Angle, Vertex, Acute Angle, Right Angle, Obtuse Angle, Straight Angle, Complementary, Supplementary, Congruent, Bisect, Angle Bisector

 

Remember:  A line extends without end in both directions.  A ray is part of a line that has an endpoint and extends without end in one direction.
Angles are formed by two rays with a common end point called a vertex.  You can find angles were lines and line segments intersect, within polygons and circles.  The symbol  < indicates an angle. You can name an angle in three ways (1) endpoint vertex endpoint - example < BAC (2) vertex - example < A or (3) by a number when it is within the angle - 

Example  1
Angles are measured in degrees (º).  They can be classified according to their measure. A protractor can be used to measure angles.  The measure of <BCD = 80º
An acute angle has a measure less than 90 degrees.  <A<90º

A right angle has a measure of exactly 90 degrees. <B=90º

An obtuse angle has a measure greater than 90degrees  but less than 180 degrees.  <C<180º

 

 A straight angle has a measure of exactly 180 degrees..  <C=180º

Two angles are complementary if their measures have a sum of 90º.

  <1 =     60º

 <2 =   +30º

90º

<1  and <2 are complementary angles.

 Two angles are supplementary if their measures have a sum of 180º.

<R =  116º

<S =  +64º

    180º

         <R and <S are supplementary.

 
-----------------------Check for Knowledge------------------------
State if the angle is acute, right, obtuse, or straight.
1.

2.

3.

4.

5.  Which angles above are complementary? 6.  Which angles above are supplementary?

Click here to check your answers!
Congruent Angles

When two angles have the same measure, we say they are congruent.  This means  the angles can fit one on top of another one.  The symbol means "is congruent to."

 We write:  <CON <GRU

We say: Angle CON is congruent to angle GRU.

Angle Bisectors

An angle bisector is a ray that separates an angle into two congruent angles.

m<ABC = 80º

Ray DB splits <ABC into two angles, <ABD and <DBC. m <CBD = m<ABC = 40º  So Ray DB is the angle bisector of  < ABC.
Test your skill by taking the Angles Quiz

Remember to ask Ms.Painter for the password!

1. Acute angle 2. Obtuse angle 3. Acute angle 4. Acute angle
5. Angle A and Angle D 6. Angle B and Angle C