Working with Angles
Section 1.6
An angle is formed by two rays with a common
endpoint.
The common endpoint is the vertex of the
angle and the rays are the
sides
of the angle.
You can name an angle by
·
its vertex or
·
a number inside the angle or
·
a point on one ray, the vertex and a point on the
other ray. When using three points to
name the angle the vertex is always name in the middle.
If at all possible we will name an angle by using
the three points
(a point on
one ray, the vertex and a point on the other ray)
Symbol:
Angles
in our Example include
1 AED or
DEA DEB or
BED DEC or
CED BEC or
CEB AEC or
CEA BEA or
AEB
The red marks show that the angles are
congruent. The
measure of the angle DEC is written " m
DEC"
BEC 
CED
You use a protractor to measure
an angle in degrees ( o )
Internet
Resources on using a protractor
·
http://www.cogtech.com/EXPLORER/protract.htm Interactive Site
·
http://www.ex.ac.uk/cimt/mepres/book7/bk7i5/bk7_5i2.htm Interactive Site
·
http://www.jaconline.com.au/maths/qld/junior/spatial/angles/skillbuilders/MS-measuring-angles-pro.pdf Great Handout with practice problems.
·
http://www.kidport.com/Grade5/Math/MeasureGeo/MeasuringAngles.htm Interactive Site
Angle Addition:
If D is in the interior
of ABC,
then m ABD
+ m DBC = m
ABC