4-2 Reflections
Warm Up
Given that ∆ABC  ∆DEF, identify a segment or
angle congruent to each of the following.
1.
2.
3.
4.
5.
6.
Holt Geometry
4-2 Reflections
Objective
Name and draw reflections.
Holt Geometry
4-2 Reflections
Try this:
• Fold a sheet of paper in half. Without opening
the paper draw a quadrilateral that is not regular
and label it ABCD.
• Turn the folded paper over and trace the image
of ABCD onto the opposite side of the paper.
Label the vertex corresponding to A as A’.
(continue with B, C, and D.)
• Open the paper and draw line l along the fold
between the two quadrilaterals. Line l is the line
of reflection.
Holt Geometry
4-2 Reflections
Try this continued:
• How do you think the measures of each side
compare with its reflection? The angles?
• Draw a line from A to A’, B to B’, C to C’ and D
to D’.
• Use a protractor to measure the angle that AA’
and l intersect.
• If you measure from A to line l, how does that
distance compare to the distance from A’ to line
l? How about for the other points?
Holt Geometry
4-2 Reflections
Example 1: Identifying Reflections
Tell whether each transformation appears to
be a reflection. Explain.
B.
A.
No; the image does not
Appear to be flipped.
Holt Geometry
Yes; the image appears
to be flipped across a
line..
4-2 Reflections
Check It Out! Example 1
Tell whether each transformation appears to
be a reflection.
a.
b.
No; the figure
does not appear to
be flipped.
Holt Geometry
Yes; the image
appears to be
flipped across a line.
4-2 Reflections
Holt Geometry
4-2 Reflections
Example 2: Drawing Reflections
Copy the triangle and the line of reflection.
Draw the reflection of the triangle across the
line.
Step 1 Through each vertex draw a line
perpendicular to the line of reflection.
Holt Geometry
4-2 Reflections
Example 2 Continued
Step 2 Measure the distance from each vertex
to the line of reflection. Locate the image of each
vertex on the opposite side of the line of
reflection and the same distance from it.
Holt Geometry
4-2 Reflections
Example 2 Continued
Step 3 Connect the images of the vertices.
Holt Geometry
4-2 Reflections
Check It Out! Example 2
Copy the quadrilateral and the line of reflection.
Draw the reflection of the quadrilateral across
the line.
Holt Geometry
4-2 Reflections
Practice Problems
1. Tell whether the transformation appears to be a
reflection.
yes
2. Copy the figure and the line of reflection. Draw the
reflection of the figure across the line.
Holt Geometry
4-2 Reflections
Other words to know
• Orientation – order of the vertices when
named (can be either clockwise or
counterclockwise)
• Image – the picture after the reflection
(preimage is the original picture)
• Line of symmetry – a line that can be
drawn through a picture so that it cuts the
picture exactly in half (use the fold test)
Holt Geometry
4-2 Reflections
Which is the image? Notice the
orientation.
S’
V
S
U
U’
T
T’
T’
R
S
T
R’
V’
Holt Geometry
S’
4-2 Reflections
Homework:
Section 4-2 #1-31
Holt Geometry