Triangle PQR is in Quadrant I of the Cartesian plane as shown in the diagram. In which quadrant will the image of triangle PQR fall when it is reflected in the x-axis (y = 0)?
Vectors, Transformations & Symmetry
Answer: B. Quadrant IV
Reflection in the x-axis (the line y = 0) sends every point (x, y) to (x, −y). The x-coordinate stays; the y-coordinate flips sign.
Triangle PQR sits in Quadrant I, so every vertex has x > 0 and y > 0. After reflection: x stays positive, y becomes negative.
(positive x, negative y) → Quadrant IV.
Why the other options are wrong: A (Quadrant II) — Q II has negative x, positive y. Would come from reflecting in the y-axis, not the x-axis. C (Quadrant I) — the original quadrant; would only happen if no reflection were applied. D (Quadrant III) — Q III has negative x and negative y. Would come from a 180° rotation about the origin (or reflecting in BOTH axes).