Download Interior and Exterior Angles

The objective of this lesson is:
•Understand the Transversal
• To identify alternate angles and corresponding
angles.
• To calculate angles between parallel lines giving a
reason for the answers
• Determine interior and exterior angles
Transversal
Definition: A line that intersects two or more lines in a
plane at different points is called a transversal.
When a transversal t intersects line n and
m, eight angles of the following types are
formed:
Exterior angles
Interior angles
Consecutive interior angles
Alternative exterior angles
Alternative interior angles
Corresponding angles
Angles and Parallel Lines
If
two parallel lines are cut by a transversal, then the
following pairs of angles are congruent.
Corresponding angles
Alternate interior angles
Alternate exterior angles
If
two parallel lines are cut by a transversal, then the
following pairs of angles are supplementary.
Consecutive interior angles
Consecutive exterior angles
Alternate Angles
• Alternate Interior Angles: Two angles that lie between
parallel lines on opposite sides of the transversal (but
not a linear pair).
 3   6,  4   5
• Alternate Exterior Angles: Two angles that lie outside
parallel lines on opposite sides of the transversal.  2 
 7,  1   8
1
3
4
5
7
2
6
8
Alternate angles
You need a pair of parallel lines.
Alternate
angles
Draw any line to cut the pair of parallel lines.
What angle is the same as the blue one?
How do you tell angles are alternate?
Alternate
angles
Look for a letter Z in any orientation.
Corresponding Angles & Consecutive Angles
Corresponding Angles: Two angles that occupy
corresponding positions.
26 15 37
1
3
5 6
7 8
2
4
48
Corresponding angles
You need a pair of parallel lines.
corresponding
angles
Draw any line to cut the pair of parallel lines.
What angle is the same as the red one?
How do you tell angles are corresponding?
corresponding
angles
Look for a letter F in any orientation.
Examples
b
c
104
a
Find the values of
the letters, give
reasons.
d
a = 76 : Angles on a straight line add up to 180
b = 76 : Corresponding angles
c = 104 : Angles on a straight line add up to 180
d =104 : Alternate angles
Examples
c
Find the values of
the letters, give
reasons.
a 68
32
68
a = 68 : Corresponding angles
b = 32 : Corresponding angles
c = 80 : Angles in a triangle add up to 180
b
Summary
• You should be able to identify alternate angles and
corresponding angles.
• You should be able to calculate angles between
parallel lines giving a reason for the answers