Rotate through quarter and half turns
Construct complete polygon images under quarter and half turns about origin, non-origin and vertex centres, keeping labels and concave boundaries in order.
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
- Subtract and add signed coordinate pairs.
- Read quarter and half turns on perpendicular axes.
- Track corresponding labels around a complete polygon.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
For a +90° turn about the origin, where does the local displacement (2,−5) go?
What you will learn
- Apply a quarter or half turn to each centre-to-vertex displacement.
- Retain fixed vertices, all named corners and the original boundary order.
- Check an image using unchanged radii and the inverse rotation.
Polygon ABC has A(1,1), B(4,1), C(2,3). In the given order, rotate about (0,0) by -90 degrees, using positive for anticlockwise. 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.
Supplied rotation -90° about (0, 0). 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.
Work from the actual pivot
A coordinate shortcut for a turn about the origin acts on a displacement from that origin. For a different centre C=(h,k), first find the local displacement (x−h,y−k), turn that displacement and then add C again. Multiplying or swapping global coordinates directly would silently change the pivot.
A +90° turn changes a local displacement (u,v) to (−v,u), a −90° turn to (v,−u), and a 180° turn to (−u,−v). These rules come from the movement of the horizontal and vertical directions around the centre. Retain both signs in every substitution.
Rotate the whole boundary
Mark every image vertex before reconnecting the outline. Join A′→B′→C′ and so on in the same named boundary order as the object. Rotating only three corners of a longer polygon leaves an incomplete figure, and replacing a concave notch by a straight edge changes the object.
A vertex at the centre has zero displacement and stays there. Other vertices keep their distances from the centre. A turn preserves the orientation of the traversal around the boundary; it does not reflect the polygon or reverse its list of corresponding labels.
Use the return movement as a check
The inverse of a rotation about C through θ is a rotation about that same C through −θ, with angles interpreted modulo 360°. A half turn therefore undoes itself. Use the inverse on more than one computed image point to check the centre as well as the signs.
A neat sketch is useful for checking the approximate quadrant of an image point, but it does not replace exact coordinate work in these quarter-turn cases. Keep integer or fractional coordinates exact, label the fixed centre separately and show the explanation connecting the local displacement to the final position.
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
Which method rotates P about a non-origin centre C?
Worked example
Polygon ABC has A(1,1), B(4,1), C(2,3). In the given order, rotate about (0,0) by -90 degrees, using positive for anticlockwise. Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Show the worked solution
- For A, subtract the pivot (0,0) to obtain the local displacement (1,1). Turn that radius through -90° with positive meaning anticlockwise; preserve its distance from the pivot. The turned local displacement is (1,-1); adding the pivot gives A′=(1,-1).
- Use the same signed turn for every vertex, then restore the centre position. The full labelled image is A′=(1,-1), B′=(1,-4), C′=(3,-2). Keep these coordinates exact.
- Reconnect the image in boundary order A′→B′→C′→A′, retaining all corners. The inverse is rotation about (0,0) through 90° (anticlockwise for the stated sign); applied to the unrounded image it returns the object and verifies both pivot and direction.
Answer A′=(1,-1), B′=(1,-4), C′=(3,-2).
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, rotate about (2,-1) by 180 degrees, using positive for anticlockwise. Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Give me a hint
Subtract the pivot before applying the quarter/half-turn rule, then restore it.
Compare my reasoning
- For A, subtract the pivot (2,-1) to obtain the local displacement (-2,1). Turn that radius through 180° with positive meaning anticlockwise; preserve its distance from the pivot. The turned local displacement is (2,-1); adding the pivot gives A′=(4,-2).
- Use the same signed turn for every vertex, then restore the centre position. The full labelled image is A′=(4,-2), B′=(1,-2), C′=(0,-4), D′=(3,-5). Keep these coordinates exact.
- Reconnect the image in boundary order A′→B′→C′→D′→A′, retaining all corners. The inverse is rotation about (2,-1) through -180° (clockwise for the stated sign); applied to the unrounded image it returns the object and verifies both pivot and direction.
A′=(4,-2), B′=(1,-2), C′=(0,-4), D′=(3,-5).
Look for these in your work
- Apply a quarter or half turn to each centre-to-vertex displacement.
- Retain fixed vertices, all named corners and the original boundary order.
- Check an image using unchanged radii and the inverse rotation.
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, rotate about (-1,2) by 270 degrees, using positive for anticlockwise. Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Give me a hint
Subtract the pivot before applying the quarter/half-turn rule, then restore it.
Compare my reasoning
- For A, subtract the pivot (-1,2) to obtain the local displacement (1,-2). Turn that radius through 270° with positive meaning anticlockwise; preserve its distance from the pivot. The turned local displacement is (-2,-1); adding the pivot gives A′=(-3,1).
- Use the same signed turn for every vertex, then restore the centre position. The full labelled image is A′=(-3,1), B′=(-3,-3), C′=(-2,-3), D′=(-2,0), E′=(0,0), F′=(0,1). Keep these coordinates exact.
- Reconnect the image in boundary order A′→B′→C′→D′→E′→F′→A′, retaining all corners. The inverse is rotation about (-1,2) through -270° (clockwise for the stated sign); applied to the unrounded image it returns the object and verifies both pivot and direction.
A′=(-3,1), B′=(-3,-3), C′=(-2,-3), D′=(-2,0), E′=(0,0), F′=(0,1).
Look for these in your work
- Apply a quarter or half turn to each centre-to-vertex displacement.
- Retain fixed vertices, all named corners and the original boundary order.
- Check an image using unchanged radii and the inverse rotation.
Polygon ABCD has A(-2,1), B(1,1), C(2,4), D(-1,3). In the given order, rotate about (1,1) by 90 degrees, using positive for anticlockwise. Construct and label its image under the stated transformation; record the corresponding vertices and explain the method.
Give me a hint
Subtract the pivot before applying the quarter/half-turn rule, then restore it.
Compare my reasoning
- For A, subtract the pivot (1,1) to obtain the local displacement (-3,0). Turn that radius through 90° with positive meaning anticlockwise; preserve its distance from the pivot. The turned local displacement is (0,-3); adding the pivot gives A′=(1,-2).
- Use the same signed turn for every vertex, then restore the centre position. The full labelled image is A′=(1,-2), B′=(1,1), C′=(-2,2), D′=(-1,-1). Keep these coordinates exact.
- Reconnect the image in boundary order A′→B′→C′→D′→A′, retaining all corners. The inverse is rotation about (1,1) through -90° (clockwise for the stated sign); applied to the unrounded image it returns the object and verifies both pivot and direction.
A′=(1,-2), B′=(1,1), C′=(-2,2), D′=(-1,-1).
Look for these in your work
- Apply a quarter or half turn to each centre-to-vertex displacement.
- Retain fixed vertices, all named corners and the original boundary order.
- Check an image using unchanged radii and the inverse rotation.
Common mistakes
- Applying an origin rule around a non-origin centre.
- Dropping a fixed vertex or a concave boundary corner.
- Changing the pivot when applying the inverse.
What can you explain now?
A polygon vertex coincides with the rotation centre. Must it be moved to make an image?
Compare with the explanation
No. Its centre-to-vertex displacement is zero, so that labelled vertex stays fixed.
The same turn acts on all displacement vectors; the zero vector remains zero without needing a direction.
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Make it stick
State the three local quarter/half-turn rules, explain the subtract-turn-add method and describe an inverse check.
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.