Reflect shapes in horizontal vertical and diagonal lines
Reflect every named vertex in an axis-parallel or diagonal mirror, checking the complete image through perpendicular equal-distance pairs and correct boundary order.
Section 5.2 · Transformation geometry
Exam scope and assessment notes
These twelve shared lessons apply to Foundation and inherited Higher for F5.2A–M; no extra Higher row is added. Keep named corners, signed turns, equivalent mirror equations, exact fractions, positive factors and the freely chosen-centre and identity exceptions. General-angle coordinates are final3dp approximations of unrounded geometry. Written explanations need human review; coordinate agreement does not certify proof or physical construction. Linear November2026/June2027 entry and regional-centre rules remain separate from modular awards. Book2 Shape and Space7 tags and Hubs66–71 are navigation only: map223–248 differs from proof222/summary247/next248, with chapter/Hub bodies unavailable.
Before you begin
- Use perpendicular distances and signed offsets.
- Interpret vertical, horizontal and diagonal line equations.
- Track named polygon boundary order.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Reflecting in x=4 sends a point with x=7 to which x-coordinate?
What you will learn
- Construct reflected points across vertical, horizontal and diagonal lines.
- Retain fixed vertices and every ordinary or concave boundary corner.
- Use equivalent line equations and the self-inverse reflection as checks.
Polygon ABC has A(1,1), B(4,1), C(2,3). In the given order, reflect in the line x=-2. Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Describe your operation, construct every named image point, and record your actual directed traces. Only the question supplies the givens. The board does not transform a shape or recover a missing parameter for you.
Both Cartesian directions have equal drawing scale. Blue is supplied geometry, amber is my actual work, purple is dirty retained work, and green is a separately gated reference. Screen size is not physical instrument calibration.
Actual boundaries retain their entered order, closure, concavity and wrong or incomplete points. No reflected corner, rotation endpoint, mirror foot or target polygon is filled automatically. Construction rays continue beyond their anchors; mirror lines continue both ways; joining segments keep their original endpoints.
Some actual points are outside this viewport and remain unchanged. The frame clips the drawing, not its mathematical domain. Pan or zoom to inspect them; no artificial arrowhead is placed at a crop intersection.
Supplied reflection in 1x + 0y = -2. This description does not generate a target boundary.
This finite fixed-case comparison is not proof marking, marks, mastery, physical construction calibration or specialist/formal assessment approval. General-angle points stay unrounded; a separately requested three-decimal written table is an approximation.
Actual operation 1
No actual construction is recorded for this action.
Choose a point slot before adding a keyboard coordinate or picking on the board. Named picks retain exact given or current clean recorded coordinates. Free picks retain their unrounded actual planar coordinates; they do not snap to an expected result.
My written coordinates, quantities and reasoning
Write both coordinates as x,y; exact fractions and finite decimals are supported.
Write both coordinates as x,y; exact fractions and finite decimals are supported.
Write both coordinates as x,y; exact fractions and finite decimals are supported.
Explain your actual correspondence, construction and conditions. A written attempt is not an automatically verified proof.
Explain your actual correspondence, construction and conditions. A written attempt is not an automatically verified proof.
Explain your actual correspondence, construction and conditions. A written attempt is not an automatically verified proof.
This sequence is optional. If you add operations, complete every chosen parameter or remove the sequence. The tool generates no inverse for you.
These original cases support mathematical self-checking. They do not award marks, mastery, proof approval, physical construction competence, specialist signoff or formal assessment readiness. Positive scale factors only; unchanged images do not uniquely recover a centre. Keep general-angle construction coordinates unrounded and separately requested written coordinates at three decimal places.
Copy the perpendicular distance across the mirror
To reflect P in a given line, draw the perpendicular from P to that mirror, then mark P′ at the same distance beyond it. The mirror is the midpoint line of PP′. A point already on the mirror stays fixed; moving it merely to make the image look separate would change the transformation.
For a vertical mirror x=h, reflection changes(x,y) to(2h−x,y). For a horizontal mirror y=k, it changes(x,y) to(x,2k−y). These rules keep the parallel coordinate and reverse the signed perpendicular offset. They apply to points on either side of the mirror.
Read diagonal mirrors as lines, not axes labels
Reflection in y=x swaps the two coordinates because horizontal and vertical offsets exchange roles across that diagonal. The equation y−x=0 describes the same line. For a mirror x+y=c, the image is(c−y,c−x); verify this with the midpoint and perpendicular joining segment rather than guessing signs.
A general line description must retain its position as well as its direction. Two parallel mirrors can produce different images. An equation such as ax+by=c should therefore be interpreted as the complete line; equivalent nonzero multiples of all three coefficients leave that line unchanged.
Reconnect the reflected figure and check it
Reflect each named vertex and join the images in the original boundary order. A reflection reverses the orientation of a boundary traversal, but it does not reverse the correspondence list or remove a concave notch. The image keeps all original side lengths and interior angles, including any reflex angle.
Reflecting the image in the same line returns the object. Use that inverse check and the equal perpendicular distances for several vertices. A final coordinate list should show every label; a partial outline or a reflected bounding box is not the complete image of the polygon.
Sources for this lesson
- Pearson Mathematics A linear specification · Issue2 · Transformation geometry Foundation printed23/physical29 and Higher inheritance printed38/physical44
- Pearson 2026/2027 International GCSE entry manual · centre regions physical3 and Mathematics A physical25
- Pearson literal second-edition book/Hub map · Book2 Shape and Space7 physical12 · navigation only
Pause and explain
A vertex lies on the given mirror line. What happens to it?
Worked example
Polygon ABC has A(1,1), B(4,1), C(2,3). In the given order, reflect in the line x=-2. Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Show the worked solution
- Use the supplied mirror: reflection in x=-2. For each moved point, place its image at equal perpendicular distance on the other side; any vertex on the mirror stays fixed.
- Applying that same line to every named vertex gives A′=(-5,1), B′=(-8,1), C′=(-6,3). Check each pair’s midpoint lies on the mirror and its nonzero joining segment is perpendicular to it.
- Join all image vertices in the original boundary order, retaining the concave corner where present. Reflection reverses the traversal orientation but preserves lengths and interior angles. The same reflection is its own inverse.
Answer A′=(-5,1), B′=(-8,1), C′=(-6,3).
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Polygon ABCD has A(0,0), B(3,0), C(4,2), D(1,3). In the given order, reflect in the line y=0. Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Give me a hint
Copy the signed perpendicular distance across the actual mirror and retain fixed points.
Compare my reasoning
- Use the supplied mirror: reflection in y=0. For each moved point, place its image at equal perpendicular distance on the other side; any vertex on the mirror stays fixed.
- Applying that same line to every named vertex gives A′=(0,0), B′=(3,0), C′=(4,-2), D′=(1,-3). Check each pair’s midpoint lies on the mirror and its nonzero joining segment is perpendicular to it.
- Join all image vertices in the original boundary order, retaining the concave corner where present. Reflection reverses the traversal orientation but preserves lengths and interior angles. The same reflection is its own inverse.
A′=(0,0), B′=(3,0), C′=(4,-2), D′=(1,-3).
Look for these in your work
- Construct reflected points across vertical, horizontal and diagonal lines.
- Retain fixed vertices and every ordinary or concave boundary corner.
- Use equivalent line equations and the self-inverse reflection as checks.
Polygon ABCDEF has A(0,0), B(4,0), C(4,1), D(1,1), E(1,3), F(0,3). In the given order, reflect in the line y=x (equivalently y-x=0). Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Give me a hint
Copy the signed perpendicular distance across the actual mirror and retain fixed points.
Compare my reasoning
- Use the supplied mirror: reflection in y=x (equivalently y−x=0). For each moved point, place its image at equal perpendicular distance on the other side; any vertex on the mirror stays fixed.
- Applying that same line to every named vertex gives A′=(0,0), B′=(0,4), C′=(1,4), D′=(1,1), E′=(3,1), F′=(3,0). Check each pair’s midpoint lies on the mirror and its nonzero joining segment is perpendicular to it.
- Join all image vertices in the original boundary order, retaining the concave corner where present. Reflection reverses the traversal orientation but preserves lengths and interior angles. The same reflection is its own inverse.
A′=(0,0), B′=(0,4), C′=(1,4), D′=(1,1), E′=(3,1), F′=(3,0).
Look for these in your work
- Construct reflected points across vertical, horizontal and diagonal lines.
- Retain fixed vertices and every ordinary or concave boundary corner.
- Use equivalent line equations and the self-inverse reflection as checks.
Polygon ABCD has A(-2,1), B(1,1), C(2,4), D(-1,3). In the given order, reflect in the line 1x+(1)y=2. Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Give me a hint
Copy the signed perpendicular distance across the actual mirror and retain fixed points.
Compare my reasoning
- Use the supplied mirror: reflection in x+y=2. For each moved point, place its image at equal perpendicular distance on the other side; any vertex on the mirror stays fixed.
- Applying that same line to every named vertex gives A′=(1,4), B′=(1,1), C′=(-2,0), D′=(-1,3). Check each pair’s midpoint lies on the mirror and its nonzero joining segment is perpendicular to it.
- Join all image vertices in the original boundary order, retaining the concave corner where present. Reflection reverses the traversal orientation but preserves lengths and interior angles. The same reflection is its own inverse.
A′=(1,4), B′=(1,1), C′=(-2,0), D′=(-1,3).
Look for these in your work
- Construct reflected points across vertical, horizontal and diagonal lines.
- Retain fixed vertices and every ordinary or concave boundary corner.
- Use equivalent line equations and the self-inverse reflection as checks.
Common mistakes
- Negating a coordinate without allowing for a shifted mirror.
- Changing the mirror line when reflecting back.
- Replacing a concave boundary by its outer box.
What can you explain now?
Why does reflecting twice in the same line return the original point?
Compare with the explanation
The first reflection reverses its perpendicular offset and the second reverses it again.
The parallel position along the mirror remains unchanged throughout, so the second equal-distance crossing returns the actual point.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Give the vertical, horizontal and y=x reflection rules, then explain the equal-distance and self-inverse checks.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.