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Reflecting in a Line

Part of the Transformations & Constructions section of Coddy's Geometry journey. Lesson 5 of 60.

Hold up your right hand to a mirror. The hand in the mirror is a left hand. A slide can never do that, because a slide keeps a shape facing the same way.

A reflection flips a shape over a line, the mirror line. Each point goes straight across the mirror, at a right angle to it. It lands the same distance away on the other side. So the mirror is halfway between a point and its image.

Here P(1, 5) is 3 above $y = 2$ . So P' is 3 below it, at (1, -1).

$Triangle PQR reflected in the dashed line y = 2$

Challenge

The mirror is the upright line x = 3. Draw the image of triangle ABC in this mirror. Drag A', B' and C' to their places.

Then press Check.

Try it yourself

$Move the shape onto its target$

Move the shape onto its target

All lessons in Transformations & Constructions

1Translations

Sliding a Shape Draw the Image The Translation Rule Recap: Translations

4Combining Moves

One Move, Then Another Order Matters Two Mirrors Name the Move Recap: Combining Moves

7Drawing on Squared Paper

Lengths by Pythagoras Perpendicular Steps Squares by Area Right Triangles by Area Midpoints on the Grid Recap: Squared Paper

10Perpendiculars and Parallels

Perpendicular From a Point Perpendicular at a Point Parallel Through a Point Tools You Have Earned Recap: Parallels

2Reflections

Reflecting in a LineThe Two Axes The Line y = x Find the Mirror Recap: Reflections

5Dilations

Scaling From a Center Shrinking a Shape Dilating About a Point Negative Scale Factors Recap: Dilations

8Compass and Straightedge

Circles Keep Distances Why the Sides Match Angles You Built A 60° Angle Recap: Equilateral Triangle

11Constructed Shapes

A Square on a Segment The Regular Hexagon Copy an Angle A Tangent From a Point Recap: Constructed Shapes