Match the distance from the mirror line
If a square is 2 spaces left of the mirror line, its match is 2 spaces right of it.
Count across from the mirror line.
Year 4
Complete a simple symmetric figure with respect to a specific line of symmetry
Use a mirror line to complete the missing half of a simple symmetric figure.
Lesson overview
Geometry - properties of shape
To complete a symmetric figure, each part on one side of the mirror line must be copied the same distance on the other side.
The shape must match too
A mirrored shape keeps the same size and shape.
Position and shape must both match.
Work one point at a time
Copy one point or square at a time.
Pairs should be equally spaced.
Build the missing half carefully.
Worked example
A point is 3 spaces to the left of a vertical mirror line. Where should the match go?
- Find the distance from the point to the mirror line.
- The point is 3 spaces away.
- The matching point must be the same distance on the other side.
- So place it 3 spaces to the right.
Round 1: Learn it
Use the mirror line and match the distance from it carefully.
Finish this round to unlock Round 2: Show you know it.
Question 1
A point is 2 spaces left of the mirror line. Where should its match go?
Question 2
What stays the same in a symmetric figure?
Question 3
A point is 4 spaces from the mirror line. How many spaces away should the matching point be?
Question 4
Which statement is correct?
yes
no
Question 5
What should you do first when finishing a symmetric figure?
Common mistakes
Watch for these as you work through the lesson.
- Putting the new part the wrong distance from the mirror line.
- Matching the side but not the shape.
- Forgetting to copy each point or square exactly.
Related topics
These ideas connect closely to this lesson.
- Identify lines of symmetry in 2-D shapes presented in different orientations.
- Describe positions on a 2-D grid as coordinates in the first quadrant.