Free graphing resources · Original practice
Drawing reflections.
Change signs, keep shape.
Reflect four point sets by changing the correct coordinate signs. Preserve vertex order, identify points on an axis and compare original and reflected shapes.
4 reflection cases.
x-axis, y-axis and both.
More ways to practice
A second case: reflect a quadrilateral over the y-axis
Take quadrilateral ABCD with A(-4, 1), B(-1, 3), C(-1, 1) and D(-4, -2). A reflection over the y-axis changes the sign of each x-coordinate and leaves each y-coordinate unchanged. The rule is (x, y) to (-x, y). Apply it to each vertex in the same order: A' is (4, 1), B' is (1, 3), C' is (1, 1) and D' is (4, -2).
Plot the original points first, then the images, and connect A to B to C to D and back to A. The image should connect A' to B' to C' to D' and back to A'. Check that the segment between each point and its image is horizontal and that the midpoint of that segment lies on the y-axis. For A and A', the midpoint is (0, 1), which is on the axis, so the pair is consistent.
- Write the reflection rule before plotting: over the y-axis, (x, y) becomes (-x, y).
- List the original vertices in order and compute each image coordinate separately.
- Plot originals and images on the same grid, then connect vertices in the listed order.
- Check one vertex pair by finding its midpoint; it must lie on the mirror line.
- Measure a matching side in the original and image with the same unit to confirm equal length.
Separate the four task types
Reflection worksheets often mix tasks that look similar but need different answers. Drawing a reflected shape asks for plotted vertices and connected segments. Judging a property asks whether lengths, angles or orientation are preserved. Computing area asks for a number in square units. A composite task applies two reflections in sequence, and the order matters.
For a composite reflection, apply the first rule to every vertex, then apply the second rule to the results. Reflecting over the x-axis then the y-axis maps (x, y) to (-x, -y), which is a rotation by 180 degrees about the origin, not a single reflection. Label intermediate points clearly so the final answer can be traced back.
- Read the task verb first: draw, decide, calculate or combine.
- For a property question, compare corresponding side lengths and angles rather than coordinates.
- For area, count grid squares or use the shoelace method with consistent units.
- For a composite task, record intermediate coordinates before applying the second rule.
Diagnostic checks before finishing
A reflected drawing can look plausible while containing one flipped sign. Run three quick checks. First, confirm every image point is the same distance from the mirror line as its original, on the opposite side. Second, confirm points that lie on the mirror line stay fixed. Third, confirm the vertex order is preserved so the shape is not accidentally rotated or mirrored twice.
Keep labels and margins readable: place vertex labels outside the shape where possible and leave space near the grid edge so reflected points are not crowded. If a point lands on an axis, state that it is unchanged rather than writing a new coordinate.
- Compare distances from the mirror line for each original and image pair.
- Identify any vertex on the mirror line and confirm it did not move.
- Trace the vertex order in both shapes and check the sequence matches.
- Recompute one coordinate by hand using the rule and compare with the plotted point.
Try this example
Reflect triangle PQR with P(2, 1), Q(5, 1) and R(2, 4) over the x-axis, then state the image coordinates and the area of the image in square units.
Show the worked explanation
Over the x-axis the rule is (x, y) to (x, -y). P' is (2, -1), Q' is (5, -1) and R' is (2, -4). The original triangle has a horizontal base PQ of length 3 units and a vertical height from R to that base of 3 units, so its area is 3 times 3 divided by 2, which is 4.5 square units. Reflection preserves area, so the image also has area 4.5 square units. Check: the midpoint of P and P' is (2, 0), which lies on the x-axis.
Common mistakes
- Changing the y-coordinate when reflecting over the y-axis. Write the rule (x, y) to (-x, y) at the top of the page and apply it to one vertex at a time.
- Connecting vertices in a different order in the image, producing a rotated-looking shape. Number the original vertices and write the same numbers beside the image points before drawing segments.
- Treating a point on the mirror line as needing a sign change. Check whether the coordinate being changed is zero; if so, the point stays fixed and should be labeled as unchanged.
Check your work
- The reflection rule is stated and applied to every vertex.
- Image coordinates are computed correctly with the correct sign change.
- Vertices are connected in the same order in original and image.
- At least one vertex pair is checked using a midpoint on the mirror line.
- Points on the mirror line are identified as unchanged.
- Units are stated for any length or area answer.
- Labels and margins remain readable and do not overlap the shape.
Questions before you start
How do I check a reflection without redrawing the whole shape?
Pick one vertex and its image, find the midpoint of the segment joining them, and confirm it lies on the mirror line. Then confirm the segment is perpendicular to that line.
What is the difference between a reflection and a rotation in these tasks?
A single reflection flips a shape across a line and reverses orientation. A rotation turns the shape about a point and preserves orientation. Two reflections can produce a rotation, so label intermediate steps.
Should area change after a reflection?
No. A reflection preserves lengths and angles, so the area in square units stays the same. If your computed areas differ, check for a plotting or counting error.