Line symmetry and reflection
Year 8 - Developing geometry…
Keywords
What do I need to be able
to do?
By the end of this unit you should be able to:
•Recognise line symmetry
•Reflect in a horizontal line
•Reflect in a vertical line
•Reflect in a diagonal line
Lines of symmetry
Mirror line (line of reflection)
Shapes can have more than
one line of symmetry….
This regular polygon (a
regular pentagon has 5 lines
of symmetry)
A circle has an infinite amount of
lines of symmetry
Mirror line: a line that passes through the center of a shape with a mirror image on either side of the line
Line of symmetry: same definition as the mirror line
Reflect: mapping of one object from one position to another of equal distance from a given line.
Vertex: a point where two or more-line segments meet.
Perpendicular: lines that cross at 90°
Horizontal: a straight line from left to right (parallel to the x axis)
Vertical: a straight line from top to bottom (parallel to the y axis)
Rhombus
two lines of symmetry
Parallelogram
No lines of symmetry
Reflect horizontally/ vertically (1 )
Reflection in a vertical line
Reflection in a horizontal line
Reflection in the line x=2
Reflection in the line y=-2
Note: a reflection
doubles the area of
the original shape
Reflection on an axis grid
Reflect horizontally/ vertically ( 2 )
All points need
to be the same
distance away
from the line of
reflection
Reflection in the line y axis –this is also a
reflection in the line x=0
Lines parallel to the x and y axis
REMEMBER
Lines parallel to the x-axis are y = ____
Lines parallel to the y-axis are x = ____
Reflect Diagonally (1 )
Points on the mirror line don’t change position
Turn your image
If you turn your image it
becomes a vertical/ horizontal
reflection (also good to check
your answer this way)
Drawing perpendicular lines
Perpendicular lines to and
from the mirror line can help
you to plot diagonal reflections
Fold along the line of symmetry to check
the direction of the reflection
Reflect Diagonally ( 2 )
This is the line y = x (every y coordinate is the
same as the x coordinate along this line)
Turn your image
If you turn your image it
becomes a vertical/ horizontal
reflection (also good to check
your answer this way)
This is the line y = - x
The x and y coordinate have the
same value but opposite sign
@whisto_maths
