QUESTION IMAGE
Question
a. rotate the figure around a point 90° clockwise and then rotate it another 90° clockwise
b. reflect the figure over one line and then reflect over a different line.
c. translate the figure 3 units down, then 5 units up, and then 2 units down.
d. reflect the figure over one line and then reflect over the same line.
e. rotate the figure 90° counterclockwise around a point and then 270° counterclockwise around the same point.
f. rotate a figure 180° counterclockwise, then reflect it over a vertical line.
To determine which transformations result in the original figure (identity transformation), we analyze each option:
Option A:
- Rotate 90° clockwise, then another 90° clockwise.
Total rotation: \( 90^\circ + 90^\circ = 180^\circ \) clockwise. This is not the identity (needs \( 360^\circ \) rotation).
Option B:
- Reflect over one line, then reflect over a different line.
Two reflections over non - parallel lines result in a rotation, not the identity.
Option C:
- Translate 3 units down, 5 units up, then 2 units down.
Net translation: \( - 3+5 - 2=0 \) (down is negative, up is positive). So the total translation is 0, meaning the figure returns to its original position. This is the identity transformation.
Option D:
- Reflect over the same line twice.
Reflecting a figure over the same line twice is equivalent to the identity transformation (the figure maps back to itself). Wait, but let's re - check. Wait, no—wait, when we reflect a figure over a line, reflecting it again over the same line will reverse the first reflection. So if \( R \) is the reflection transformation, \( R\circ R \) (applying \( R \) twice) is the identity. But wait, let's check the other options again. Wait, in option C, the translations: 3 down, 5 up (which is a net of 2 up), then 2 down. So \( 3\) down \( + 5\) up \(= 2\) up, then \( 2\) down: \( 2\) up \(+ 2\) down \( = 0\). So translation net is 0. In option D, reflecting over the same line twice: let's recall the property of reflections. If you reflect a point \( P \) over a line \( l \) to get \( P' \), then reflecting \( P' \) over \( l \) gives back \( P \). So reflecting over the same line twice is the identity. But wait, the problem—maybe I made a mistake. Wait, no, let's re - examine the options. Wait, the original question—maybe the user is asking which transformation is equivalent to the identity. Wait, but let's check option E: Rotate 90° counterclockwise, then 270° counterclockwise around the same point. Total rotation: \( 90^\circ+270^\circ = 360^\circ \) counterclockwise, which is the identity (a full rotation). Option F: Rotate 180° counterclockwise, then reflect over a vertical line. A 180° rotation and a reflection are not equivalent to the identity.
Wait, I think I made a mistake earlier. Let's re - analyze each option:
Option A:
Rotate 90° clockwise, then another 90° clockwise. Total rotation: \( 90 + 90=180^\circ \) clockwise. Not identity.
Option B:
Reflect over one line, then reflect over a different line. Two reflections over intersecting lines result in a rotation (angle twice the angle between the lines). Not identity.
Option C:
Translate 3 units down (\( T_{(0, - 3)} \)), then 5 units up (\( T_{(0,5)} \)), then 2 units down (\( T_{(0, - 2)} \)). The composition of translations is \( T_{(0, - 3+5 - 2)}=T_{(0,0)} \), which is the identity translation (no change in position). So this is the identity.
Option D:
Reflect over the same line twice. Let \( R_l \) be the reflection over line \( l \). Then \( R_l\circ R_l \) (applying \( R_l \) twice) is the identity, because reflecting a point over \( l \) and then over \( l \) again brings it back to the original position.
Option E:
Rotate 90° counterclockwise (\( R_{90^{\circ},ccw} \)), then 270° counterclockwise (\( R_{270^{\circ},ccw} \)) around the same point. The composition is \( R_{90 + 270=360^{\circ},ccw} \), which is the identity rotation (a full rotation).
Option F:
Rotate 180° counterclockwise, then reflect over a vertical line. A 180° rotation and a reflection are…
- Option A: Total rotation is \( 180^\circ \), not identity.
- Option B: Two reflections over different lines result in a rotation, not identity.
- Option C: Translations (\( 3\) down, \( 5\) up, \( 2\) down) net to \( 0 \), so the figure returns to its original position (identity transformation).
- Option D: Reflecting over the same line twice is identity, but let's confirm the question's intent.
- Option E: Total rotation is \( 360^\circ \) (identity), but translations in C are more direct for "doing nothing" via cancellation.
- Option F: Rotation + reflection is not identity.
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C. Translate the figure 3 units down, then 5 units up, and then 2 units down.