Understand Line Segment Transformation Properties

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8th Grade Math › Understand Line Segment Transformation Properties

Questions 1 - 10
1

Segment $$AB$$ has endpoints $A(1,2)$ and $B(4,6)$. The segment is translated by $(+3,+2)$ to form $A'B'$. What is the length of $A'B'$?

$10$

$5$

$7$

$\sqrt{29}$

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length $d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$ transforms to A'B' with equal length $d' = d$. Example: AB from (1,2) to (4,6) has length $\sqrt{9+16} = 5$, translation by (+3,+2) gives A'(4,4) to B'(7,8) with length $\sqrt{9+16} = 5$ unchanged. Property holds for all three transformations (move/flip/turn but don't resize). For this specific translation, original AB from (1,2) to (4,6) has length $\sqrt{(4-1)^2 + (6-2)^2} = \sqrt{9+16} = 5$, and after adding (+3,+2), A'(4,4) to B'(7,8) has length $\sqrt{(7-4)^2 + (8-4)^2} = \sqrt{9+16} = 5$, confirming preservation. The correct answer is 5, as the translation shifts the position but keeps the distance between points the same. Common errors include miscalculating the distance as $\sqrt{ (4+1)^2 + (6+2)^2 } = \sqrt{25+64} = \sqrt{89}$ or confusing with vector addition leading to wrong lengths like 7 or 10. To verify: (1) calculate original length using distance formula, (2) apply translation by adding (3,2) to each coordinate, (3) calculate image length with new points, (4) compare—they are equal. All rigid transformations preserve length because they are isometries, maintaining distances while changing position or orientation but not size.

2

Segment $\overline{ST}$ has endpoints $S(0,0)$ and $T(6,8)$. It is reflected over the $x$-axis to form $\overline{S'T'}$. What is the length of $\overline{S'T'}$?

$8$ units

$10$ units

$14$ units

$\sqrt{28}$ units

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. Example: AB from (1,2) to (4,6) has length √(9+16)=5, translation by (+3,+2) gives A'(4,4) to B'(7,8) with length √(9+16)=5 unchanged. Property holds for all three transformations (move/flip/turn but don't resize). For this reflection over the x-axis, original ST length is √[(6-0)² + (8-0)²] = √[36+64] = 10, and after reflection, S'(0,0) to T'(6,-8) has length √[(6-0)² + (-8-0)²] = √[36+64] = 10, confirming preservation. The length is 10 units, unchanged. A common error is calculating only partial differences, like √[36+16]=√52 or something leading to 14 if adding wrong. To verify: (1) calculate original length, (2) negate y-coordinates, (3) calculate image length, (4) compare—equal. All rigid transformations preserve length because they maintain distances (isometries: distance-preserving transformations)—the segment flips but not size.

3

Which transformation always preserves the length of a line segment (keeps it the same) on a coordinate plane?

A rotation

A reflection

A translation

All of the above

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. Example: AB from (1,2) to (4,6) has length √(9+16)=5, translation by (+3,+2) gives A'(4,4) to B'(7,8) with length √(9+16)=5 unchanged. Property holds for all three transformations (move/flip/turn but don't resize). This general question confirms that translations, rotations, and reflections all preserve lengths, as they are rigid motions. This verifies the concept, as the correct answer is all of the above. A common error is thinking only one preserves length (e.g., claiming reflections change it), confusing with non-rigid like dilations. Verifying: (1) recall definitions, (2) apply each transformation to a sample segment, (3) check lengths equal, (4) confirm for all. All rigid transformations preserve length because they maintain distances (isometries: distance-preserving transformations)—segment moves position/orientation but not size. Common errors: assuming non-Euclidean metrics or misapplying rules leading to false length changes.

4

Segment $\overline{LM}$ has endpoints $L(1,4)$ and $M(6,4)$. It is rotated $180^\circ$ about the origin to form $\overline{L'M'}$. What is the length of $\overline{L'M'}$?

10 units

9 units

1 unit

5 units

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. Example: AB from (1,2) to (4,6) has length √(9+16)=5, translation by (+3,+2) gives A'(4,4) to B'(7,8) with length √(9+16)=5 unchanged. Property holds for all three transformations (move/flip/turn but don't resize). For this 180° rotation, original LM length is √[(6-1)² + (4-4)²] = √[25+0] = 5, and after rotation, L'(-1,-4) to M'(-6,-4) has length √[(-6 - (-1))² + (-4 - (-4))²] = √[25+0] = 5, verifying preservation. The length is 5 units, as rotations keep distances. A common error is doubling differences, leading to 10 units. To verify: (1) calculate original length, (2) apply (x,y) to (-x,-y), (3) calculate image length, (4) compare—equal. All rigid transformations preserve length because they maintain distances (isometries: distance-preserving transformations)—the segment turns but not size.

5

Segment $\overline{EF}$ has endpoints $E(2,1)$ and $F(2,6)$. It is rotated $90^\circ$ counterclockwise about the origin to form $\overline{E'F'}$. What is the length of $\overline{E'F'}$?

6 units

4 units

10 units

5 units

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. Example: AB from (1,2) to (4,6) has length √(9+16)=5, translation by (+3,+2) gives A'(4,4) to B'(7,8) with length √(9+16)=5 unchanged. Property holds for all three transformations (move/flip/turn but don't resize). For this specific 90° counterclockwise rotation about the origin, original EF from (2,1) to (2,6) has length √((2-2)²+(6-1)²)=√(0+25)=5, and after rotation, E' is (-1,2) and F' is (-6,2), with length √((-6-(-1))²+(2-2)²)=√(25+0)=5. This verifies the length preservation, as the correct answer is 5 units, matching the unchanged distance. A common error is claiming rotation changes the length (e.g., 5 becomes 4 or 6 from misrotation), using wrong distance like |6-1| + |2-2| = 5 but altering to 10, or incorrect rotation rule like clockwise giving wrong points then wrong length. Verifying: (1) calculate original length with distance formula, (2) apply rotation using (x,y) to (-y,x), (3) calculate image length with the same formula, (4) compare (should equal). All rigid transformations preserve length because they maintain distances (isometries: distance-preserving transformations)—segment moves position/orientation but not size.

6

A line segment on a coordinate grid has endpoints $G(-3,1)$ and $H(1,4)$. It is translated by $(-2,+5)$ to form $G'H'$. Which statement is true?

The length changes only if the segment is diagonal.

The length stays the same because translations preserve distance.

The length becomes negative because of the $-2$ in the translation.

The length increases because both coordinates change.

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. For GH from (-3,1) to (1,4), original length √((1 - (-3))² + (4-1)²) = √(16+9) = 5; after translation (-2,+5), G'(-5,6) to H'(-1,9), length √((-1 - (-5))² + (9-6)²) = √(16+9) = 5. The true statement is that length stays the same because translations preserve distance. Errors like claiming length becomes negative from the -2 or changes only for diagonal segments ignore preservation property. To verify: (1) calculate original length, (2) add translation vector to coordinates, (3) calculate image length, (4) compare—identical. All rigid transformations are isometries, preserving distances while shifting position.

7

Segment $\overline{EF}$ has endpoints $E(2,-1)$ and $F(2,4)$. It is rotated $90^\circ$ counterclockwise about the origin to form $\overline{E'F'}$. What is the length of $\overline{E'F'}$?

3 units

It cannot be determined without graphing.

5 units

6 units

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. Example: AB from (1,2) to (4,6) has length √(9+16)=5, translation by (+3,+2) gives A'(4,4) to B'(7,8) with length √(9+16)=5 unchanged. Property holds for all three transformations (move/flip/turn but don't resize). For this 90° counterclockwise rotation, original EF length is √[(2-2)² + (4 - (-1))²] = √[0+25] = 5, and after rotation, E'(1,2) to F'(-4,2) has length √[(-4-1)² + (2-2)²] = √[25+0] = 5, verifying preservation. The length is 5 units, unchanged by rotation. A common error is misapplying rotation rules, leading to wrong points and claiming 3 or 6 units. To verify: (1) calculate original length, (2) apply rotation using (x,y) to (-y,x), (3) calculate image length, (4) compare—equal. All rigid transformations preserve length because they maintain distances (isometries: distance-preserving transformations)—the segment turns but not size.

8

A student draws segment $QR$ from $Q(-4,-2)$ to $R(-1,2)$. Then the student translates it by $(+5,-3)$ and reflects the result over the $y$-axis to get $Q''R''$. What is the length of $Q''R''$?

$5$

$10$

$8$

$\sqrt{7}$

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. For QR from (-4,-2) to (-1,2), original length √((-1 - (-4))² + (2 - (-2))²) = √(9+16) = 5; after translation (+5,-3) to (1,-5) and (4,-1), then y-axis reflection to (-1,-5) and (-4,-1), length √((-4 - (-1))² + (-1 - (-5))²) = √(9+16) = 5. Correct length is 5, as multiple transformations preserve distance. Error: incorrect order or rules, leading to wrong points and lengths like 8. Verify: (1) original length, (2) apply translation then reflection, (3) image length, (4) same. Isometries compose to preserve lengths.

9

Segment $NP$ has endpoints $N(2,7)$ and $P(6,2)$. It is reflected over the line $y=x$ to form $N'P'$. What is the length of $N'P'$?

$\sqrt{41}$

$9$

$41$

$\sqrt{5}$

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. For NP from (2,7) to (6,2), original length √((6-2)² + (2-7)²) = √(16+25) = √41; after y=x reflection, N'(7,2) to P'(2,6), length √((2-7)² + (6-2)²) = √(25+16) = √41. Correct length is √41, verified by swapped coordinates yielding same differences. Error: confusing with distance as sum, getting 9 instead. Verify by: (1) original distance, (2) swap x and y, (3) new distance, (4) equal. Isometries flip but keep size.

10

A student says: “If you rotate a segment $90^\circ$, its length might change because it points in a different direction.” Which statement best corrects the student?

The student is incorrect; rotations are rigid transformations that preserve length.

The student is incorrect; rotations always double the length.

The student is correct only if the rotation is about the origin.

The student is correct; diagonal segments change length when rotated.

Explanation

This question tests understanding that rotations, reflections, and translations preserve line segment lengths—rigid transformations move segments without stretching or compressing. Rigid transformations (rotation, reflection, translation) preserve distances: segment AB with length d=√((x₂-x₁)²+(y₂-y₁)²) transforms to A'B' with equal length d'=d. Example: AB from (1,2) to (4,6) has length √(9+16)=5, translation by (+3,+2) gives A'(4,4) to B'(7,8) with length √(9+16)=5 unchanged. Property holds for all three transformations (move/flip/turn but don't resize). The student's claim is incorrect because rotations preserve lengths regardless of direction; for example, rotating (0,0) to (3,4) by 90° gives (0,0) to (-4,3), both lengths √[9+16]=5. The best correction is that rotations are rigid transformations that preserve length. A common error is thinking direction changes length, like claiming it doubles. To verify the concept: (1) calculate original length, (2) apply rotation rules, (3) calculate image length, (4) compare—always equal for rigid motions. All rigid transformations preserve length because they maintain distances (isometries: distance-preserving transformations)—the segment turns but not size.

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