A Two lines are sufficient to define the line of reflection. The mirror line bisects the line (divides it into two equal parts).Ĭonstruct the line that reflects shape A onto its image A’. A B C D A’ B’ C’ D’ object image mirror line or axis of reflection Stress that the mirror line is always perpendicular (at right angles) to any line connecting a point to its image. D’ mirror line or axis of reflection The image is congruent to the original shape.Ħ Reflecting shapes If we draw a line from any point on the object to its image, the line forms a perpendicular bisector to the mirror line. Define the word congruent to mean the same shape and size. The image of a shape can be produced by any transformation including rotations, translations and enlargements, as well as reflections. A B C D A’ B’ object image C’ Explain that we call the original shape the object and the reflected shape the image. Reflecting shapes If we reflect the quadrilateral ABCD in a mirror line, we label the image quadrilateral A’B’C’D’. For example, Each point in the image must be the same distance from the mirror line as the corresponding point of the original object.ĥ The image is congruent to the original shape. We can find the order of rotational symmetry using tracing paper.Ĥ Reflection An object can be reflected in a mirror line or axis of reflection to produce an image of the object. Discuss what it means for a shape to have rotational symmetry. Only objects that have rotational symmetry of two or more are said to have rotational symmetry. If the order of rotational symmetry is one, then the object has to be rotated through 360° before it fits onto itself again. The order of rotational symmetry is the number of times the object fits onto itself during a 360° turn.
one line of symmetry four lines of symmetry no lines of symmetryĪsk a volunteer to come to the board and drag the vertices to make the shape symmetrical about the given mirror line.ģ Rotational symmetry An object has rotational symmetry if it fits exactly onto itself when it is turned about a point at its centre. The last example has rotational symmetry but not line symmetry. Explain that if you fold along a line of symmetry the two sides should match up exactly. Some pupils may find it easier to visualize a line of symmetry if they visualize it as a fold line rather than a mirror line. The mirror line is called a line of symmetry. 1 Reflection symmetry If you can draw a line through a shape so that one half is the mirror image of the other then the shape has reflection or line symmetry.
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