Crack the Mirror Test

One tiny corner can expose a fake mirror image. How? Every point must cross one straight line... then land at exactly the matching distance on the other side.

A line of symmetry is a mirror line. Fold the page along it, and one half lands exactly on the other. Watch the blue triangle fold across the vertical line. Each corner travels straight across to its partner. Nothing slides up or down. On a square grid, count from the mirror line. This corner is three squares left, so its reflection belongs three squares right, on the SAME row. Draw a horizontal guide. Repeat for every corner, then join the reflected points in matching order. If coordinates appear, read across first, then up. The horizontal coordinate comes before the vertical coordinate. Two, five is not five, two. Across a vertical mirror line, the horizontal position changes, while the height stays fixed. The image faces the opposite way because it is reflected, not turned.

Let's work through an example. On a coordinate grid, the vertical mirror line is x equals four. A triangle has vertices at one, two; three, four; and one, six. Complete its reflection across the line, and give the three new coordinates. Start with one, two. It is three squares left of x equals four, so move three squares right, staying on row two. The reflected point is seven, two. Next, three, four is one square left. Its partner is one square right, at five, four. The final vertex, one, six, is three squares left, so its reflection is seven, six. Join seven, two; five, four; and seven, six. Now check. Each pair shares a row and sits equally far from the mirror line. The answer is seven, two; five, four; and seven, six.

Remember: cross the mirror line, keep the matching distance, and stay on the same row for a vertical line. Read coordinates across, then up. You can spot symmetry - and complete a reflection with confidence!