Question

What work would I do to answer this question?

Answer 1

9514 1404 393

Explanation:

As you know, the correct answer choices are marked.

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Translation can be accomplished by reflecting across two parallel lines. The amount of translation is double (twice) the distance between the lines. Any two lines with the same spacing will give the same translation.

Here, the translation is 4 up and 4 right. The amount by which each point is translated is 4√2 units in the direction "northeast", that is, along a line with a slope of 4/4 = 1.

Any line of reflection is a perpendicular bisector of the segment joining the original point and its image. This means we need to identify two lines that have a slope of -1 and that are separated by (4√2)/2 = 2√2 units.

The attachment shows that two lines with this slope that have a separation of 2√2 will have y-intercepts that differ by 4. (The lines shown happen to be the correct answer choices.)

The offered choices of lines have y-intercepts of {5, 6} and {10, 12}. The only pair of lines with y-intercepts that differ by 4 are y=-x+6 and y=-x+10.

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Additional comment

We have made sort of a qualitative argument for the correct answer. If you like, you can say that the two lines of reflection each cause the image to be located halfway to its destination. That mean, for example, for point R(2,2), the first image point is R'(4,4). The line of reflection, as we said above, is the perpendicular bisector of this. It will have a slope of -1 and go through the point (3, 3), so its equation is ...

  y -3 = -1(x -3)   ⇒   y = -x +6

Similarly, the second (final) image point is R''(6,6). We can find the other line of reflection to be one that has a slope of -1 and goes through the point (5, 5). Its equation is ...

  y -5 = -1(x -5)   ⇒   y = -x +10

These are two of the equations that are offered as answer choices, so should be selected.

As we said at the beginning, any lines with this spacing will do. We cannot presume at the start that each line of reflection will move the image half the distance.