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Part 1
Prove the following theorem.
Any rigid motion can be expressed as a composition of reflections.
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Part 1
Any rigid motion must be a\u200b translation, a\u200b reflection, a\u200b rotation, or a glide reflection. Consider these one at a time. Which of the following is true of\u200b translations?
A.
Any translation can be expressed as a composition of reflections across three lines whose single intersection point is halfway between any point and its image.
B.
Any translation can be expressed as a composition of reflections across two parallel lines.
C.
Any translation can be expressed as a composition of reflections across two perpendicular lines that intersect halfway between any point and its image.
D.
Any translation can be expressed as a composition of reflections across three parallel lines.
E.
Any translation can be expressed as a composition of reflections across two lines whose intersection point is halfway between any point and its image.
1. **State the problem:** We need to determine which statement correctly describes how any translation can be expressed as a composition of reflections.
2. **Recall the theorem:** Any rigid motion (isometry) in the plane can be expressed as a composition of reflections.
3. **Focus on translations:** A translation moves every point by the same distance in the same direction.
4. **Key fact about translations and reflections:**
- A translation can be represented as the composition of two reflections across two parallel lines.
- The distance between these two parallel lines is half the magnitude of the translation vector.
5. **Explanation:**
- Reflecting a point across the first line moves it to an intermediate position.
- Reflecting this image across the second parallel line moves it to the final translated position.
- The composition of these two reflections results in a translation.
6. **Check the options:**
- A: Three lines with a single intersection point — incorrect for translation.
- B: Two parallel lines — correct.
- C: Two perpendicular lines — this produces a rotation, not a translation.
- D: Three parallel lines — unnecessary and incorrect.
- E: Two lines intersecting at a point — this produces a rotation, not a translation.
**Final answer:**
**B. Any translation can be expressed as a composition of reflections across two parallel lines.**