Answer:
- dilation by a factor of 1/2
- reflection over the line y = -x
Step-by-step explanation:
You want to find a sequence of transformations that will map ∆PZY to ∆RST as shown in the figure.
Dilation
First of all, we notice the triangles are not the same size. We can find the required dilation factor by finding the ratio of corresponding side lengths.
The first two letters in the triangle designators in the similarity statement are PZ and RS. Since RS is the target size, the dilation factor needs to be ...
k = RS/PZ
Counting grid squares in the figure, we see this ratio is ...
k = 2/4 = 1/2
Dilation by a factor of 1/2 will make triangle PZY the same size as ∆RST.
Using the origin as the center of the dilation, all of the points of ∆PZY move to a position that is half their original distance from the origin. The dilated triangle is purple triangle P'Z'Y' in the attached figure.
Reflection
When we name the vertices of ∆PZY or ∆P'Z'Y', we are naming them in counterclockwise order. The vertices of ∆RST are being named in clockwise order. This reversal of the sequence of vertices is caused by a reflection over a line.
The line of reflection will be halfway between a vertex and its reflected image. For example, reflecting ∆P'Z'Y' across the y-axis give ∆P"Z"Y", as shown in the attached figure. This reflection requires an additional transformation to map P"Z"Y" to RST.
We want to map P' to R, Z' to S, and Y' to T. As it happens the line halfway between these pairs of points is the line y=-x, the dashed line shown in the attachment.
Reflection across the line y = -x will map ∆P'Z'Y' to ∆RST.
This transformation, together with the dilation above, will map the ∆PZY to ∆RST as required.
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Rotation
If we use the reflection over the y-axis described above, we are faced with mapping ∆P"Z"Y" to ∆RST. We notice that segment P"Z" points "east" (in the +x direction). We want to map this segment to RS, which points "north" (in the +y direction). That can be accomplished by rotating ∆P"Z"Y" 90° counterclockwise about the origin.
So, another sequence of transformation that will make the required mapping is ...
- dilation by a factor of 1/2
- reflection across the y-axis
- rotation 90° CCW
The order of reflection and rotation is important. The dilation can occur anywhere in the sequence.
Alternate solution
Perhaps you realize that we could reflect the figure across the x-axis instead of the y-axis. In that case, the rotation needs to be 90° CW to complete the mapping. That is, yet another sequence could be ...
- dilation by a factor of 1/2
- reflection across the x-axis
- rotation 90° CW
If you decide you want to do the rotation before the reflection, then the direction of rotation is reversed.
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Additional comment
Figuring the answer to these mapping problems requires a certain amount of spatial sense. It can help to cut a figure from paper or cardboard and label the vertices. Then you can translate it, rotate it, flip it over, to see what works to get it to the right position. If you have a little trouble with the rotation, you can stick a pin through the center of rotation so your figure keeps its appropriate distance and orientation relative to that center.
Tracing paper and/or transparencies can be helpful for these exercises.
