Learn and verify three important properties of geometrical translations.
When you translate something in geometry, you're simply moving it around. You don't distort it in any way. If you translate a segment, it remains a segment, and its length doesn't change. Similarly, if you translate an angle, the measure of the angle doesn't change.
These properties may seem obvious, but they're important to keep in mind later on when we do proofs. To make sure we understand these properties, let's walk through a few examples.

Property 1: Line segments are taken to line segments of the same length.

Translate the following line segment by open angle, 2, comma, minus, 7, close angle.
What is the length of the source—the segment before the translation?
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, p, i or 2, slash, 3, space, p, i
What is the length of the image—the segment after the translation?
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, p, i or 2, slash, 3, space, p, i

In order to translate the segment by open angle, 2, comma, minus, 7, close angle, we move it two units to the right and seven units down.
By counting the number of units between the endpoints of the line segments, we see that both the source and the image are eight units long.
As you can see for yourself, the source and the image are both line segments with the same length. This is true for any line segment that goes under any translation.

Property 2: Angles are taken to angles of the same measure.

Translate the following angle by open angle, 5, comma, minus, 6, close angle.
Has the measure of the angle changed after the translation?
Choose 1 answer:
Choose 1 answer:

In order to translate the angle by open angle, 5, comma, minus, 6, close angle, we move it five units to the right and six units down.
As the widget shows, the source angle's measure is 45degree, and the image angle's measure is 45degree as well. Therefore, the measure of the angle has not changed.
As you can see for yourself, the source angle and the image angle have the same measure. This is true for any angle that goes under any translation.

Property 3: Lines are taken to lines, and parallel lines are taken to parallel lines.

Translate the following pair of parallel lines by open angle, minus, 4, comma, 3, close angle.
Are the two image lines parallel?
Choose 1 answer:
Choose 1 answer:

In order to translate the lines by open angle, minus, 4, comma, 3, close angle, we move them four units to the left and three units up.
We know the image lines are parallel because they have a vertical distance of four units in two different locations.
As you can see for yourself, each line is taken to another line, and the image lines remain parallel to each other. This is true for any line—or lines—that go under any translation.

Conclusion

We found that translations have the following three properties:
  • line segments are taken to line segments of the same length;
  • angles are taken to angles of the same measure; and
  • lines are taken to lines and parallel lines are taken to parallel lines.
This makes sense because a translation is simply like taking something and moving it up and down or left and right. You don't change the nature of it, you just change its location.
It's like taking the elevator or going on a moving walkway: you start in one place and end in another, but you are the same as you were before, right?