Understand Similarity Through Transformations
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8th Grade Math › Understand Similarity Through Transformations
Rectangle $R$ is $2\text{ cm}$ by $4\text{ cm}$. Rectangle $S$ is $3\text{ cm}$ by $5\text{ cm}$. Are the rectangles similar?
No, because the side ratios are not equal: $2/3\ne 4/5$.
Yes, because you can translate and rotate one rectangle to match the other.
No, because dilations change angle measures.
Yes, all rectangles are similar.
Explanation
Tests understanding similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures: same shape, proportional sides (corresponding sides have equal ratios forming scale factor k), equal corresponding angles. Requires dilation: rigid transformations (rotation, reflection, translation) preserve size giving congruence (k=1), dilation scales by factor k creating different sizes (k=2 doubles all lengths, k=1/2 halves). Sequence: typically "dilate by k from center, then rotate/reflect/translate as needed to position" or variations—dilation creates size difference, others adjust position/orientation. [Example: triangle with sides 3-4-5 similar to triangle with sides 6-8-10, check proportionality: 6/3=8/4=10/5=2 (equal ratios, scale factor k=2), sequence could be "dilate by 2 from origin" giving similar triangle 2× larger, then translate/rotate to match position if needed]. The rectangles are not similar because the side ratios are not equal: 2/3 ≠ 4/5 for corresponding sides. A common error is assuming all rectangles are similar or that rigid transformations alone can make them similar without checking proportionality. Checking similarity: (1) measure corresponding sides (side AB corresponds to A'B', BC to B'C', etc.), (2) calculate ratios (AB/A'B', BC/B'C', CA/C'A'), (3) verify equal (all ratios same value k? yes→similar with scale factor k), (4) check angles if uncertain (corresponding angles equal? yes→similar). Transformation sequence: identify scale factor (ratio of sides: k=6/3=2), describe dilation (dilate by 2 from origin), add rigid transformations if needed (rotate, reflect, translate to match position). Congruence is similarity with k=1 (special case: same size and shape). Mistakes: forgetting dilation (trying to use only rigid for different sizes—impossible), inverting scale factor (using smaller/larger instead of larger/smaller), claiming proportional when ratios differ (not checking all pairs).
Triangle $ABC$ has vertices $A(1,1)$, $B(4,1)$, and $C(1,3)$. Triangle $A'B'C'$ has vertices $A'(2,2)$, $B'(8,2)$, and $C'(2,6)$. Which sequence of transformations maps triangle $ABC$ to triangle $A'B'C'$?
Translate right 1 and up 1, then rotate $90^\circ$ counterclockwise about the origin
Dilate by scale factor $2$ about the origin, then translate right 0 and up 0 (no translation)
Translate right 1 and up 1, then dilate by scale factor $2$ about the origin
Dilate by scale factor $2$ about the origin, then translate right 0 and up 0
Explanation
This question tests understanding of similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures have the same shape with proportional sides where corresponding sides have equal ratios forming scale factor k, and equal corresponding angles; it requires dilation because rigid transformations like rotation, reflection, and translation preserve size giving congruence with k=1, while dilation scales by factor k creating different sizes, such as k=2 doubling all lengths or k=1/2 halving them, with sequences typically involving dilate by k from a center then rotate, reflect, or translate as needed to position, where dilation creates the size difference and others adjust position or orientation. For example, a triangle with sides 3-4-5 is similar to one with sides 6-8-10, checking proportionality: 6/3=8/4=10/5=2 for equal ratios with scale factor k=2, and a sequence could be dilate by 2 from the origin giving a similar triangle twice as large, then translate or rotate to match position if needed. In this case, dilating triangle ABC by scale factor 2 about the origin maps A(1,1) to (2,2), B(4,1) to (8,2), and C(1,3) to (2,6), exactly matching A'B'C' with no additional translation needed, so choice C is correct. A common error is choosing a sequence without dilation or misordering transformations, like translating first then dilating in choice D, which would not produce the correct coordinates since dilation after translation scales the translation vector as well. To check similarity and transformations, identify corresponding points, calculate the scale factor from ratios like distance AB=3 to A'B'=6 giving k=6/3=2, verify it for all sides, and confirm angles are preserved; here, the sequence is dilation by 2 from the origin with no rigid transformations needed. Remember, congruence is similarity with k=1 as a special case of same size and shape, and mistakes include forgetting dilation for size changes or inverting the scale factor.
Triangle $JKL$ has side lengths $4$, $6$, and $8$. Triangle $MNO$ has side lengths $6$, $9$, and $12$. Are the triangles similar? If yes, what is the scale factor from $\triangle JKL$ to $\triangle MNO$?
No; the triangles are not similar because $4+6\ne 8$.
No; the triangles are not similar because translations are required.
Yes; scale factor $k=\tfrac{2}{3}$.
Yes; scale factor $k=\tfrac{3}{2}$.
Explanation
This question tests understanding of similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures have the same shape with proportional sides (corresponding sides have equal ratios forming scale factor k) and equal corresponding angles; it requires dilation since rigid transformations (rotation, reflection, translation) preserve size giving congruence (k=1), while dilation scales by factor k creating different sizes (k=2 doubles all lengths, k=1/2 halves); the sequence is typically 'dilate by k from center, then rotate/reflect/translate as needed to position' or variations—dilation creates size difference, others adjust position/orientation. For example, a triangle with sides 3-4-5 is similar to a triangle with sides 6-8-10; check proportionality: 6/3=8/4=10/5=2 (equal ratios, scale factor k=2), sequence could be 'dilate by 2 from origin' giving similar triangle 2× larger, then translate/rotate to match position if needed. The triangles are similar with scale factor 3/2 from JKL to MNO since 6/4=3/2, 9/6=3/2, 12/8=3/2, making choice A correct. A common error is using sum instead of ratio (like 4+6≠8) or thinking translations prevent similarity. To check similarity: (1) measure corresponding sides (assume 4 to 6, 6 to 9, 8 to 12), (2) calculate ratios (6/4=1.5, etc.), (3) verify equal (yes, k=3/2), (4) angles equal by proportionality. Mistakes include inverting k to 2/3 or claiming not similar due to translations.
Polygon $A$ is obtained from polygon $B$ by a dilation with scale factor $1$. Which statement is true?
The polygons are congruent, and congruent figures are a special case of similar figures.
The polygons are not similar because dilation must have scale factor greater than $1$.
The polygons are not congruent because dilation always changes size.
The polygons are similar but not congruent.
Explanation
Tests understanding similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor $k \neq 1$. Similar figures: same shape, proportional sides (corresponding sides have equal ratios forming scale factor $k$), equal corresponding angles. Requires dilation: rigid transformations (rotation, reflection, translation) preserve size giving congruence ($k=1$), dilation scales by factor $k$ creating different sizes ($k=2$ doubles all lengths, $k=1/2$ halves). Sequence: typically "dilate by $k$ from center, then rotate/reflect/translate as needed to position" or variations—dilation creates size difference, others adjust position/orientation. [Example: triangle with sides 3-4-5 similar to triangle with sides 6-8-10, check proportionality: $6/3=8/4=10/5=2$ (equal ratios, scale factor $k=2$), sequence could be "dilate by 2 from origin" giving similar triangle $2 \times$ larger, then translate/rotate to match position if needed]. The polygons are congruent since dilation by $k=1$ leaves size unchanged, and congruence is a special case of similarity. A common error is thinking dilation with $k=1$ changes size or that similarity requires $k>1$. Checking similarity: (1) measure corresponding sides (side AB corresponds to A'B', BC to B'C', etc.), (2) calculate ratios (AB/A'B', BC/B'C', CA/C'A'), (3) verify equal (all ratios same value $k$? yes→similar with scale factor $k$), (4) check angles if uncertain (corresponding angles equal? yes→similar). Transformation sequence: identify scale factor (ratio of sides: $k=6/3=2$), describe dilation (dilate by 2 from origin), add rigid transformations if needed (rotate, reflect, translate to match position). Congruence is similarity with $k=1$ (special case: same size and shape). Mistakes: forgetting dilation (trying to use only rigid for different sizes—impossible), inverting scale factor (using smaller/larger instead of larger/smaller), claiming proportional when ratios differ (not checking all pairs).
Rectangle $R$ has side lengths $2$ cm by $4$ cm. Rectangle $S$ has side lengths $3$ cm by $5$ cm. Are rectangles $R$ and $S$ similar?
Yes, all rectangles are similar
Yes, because $2+4=3+5$
No, because rectangles cannot be similar unless they are squares
No, because $\frac{2}{3} \ne \frac{4}{5}$ so the side lengths are not proportional
Explanation
This question tests understanding of similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures have the same shape with proportional sides where corresponding sides have equal ratios forming scale factor k, and equal corresponding angles; it requires dilation because rigid transformations like rotation, reflection, and translation preserve size giving congruence with k=1, while dilation scales by factor k creating different sizes, such as k=2 doubling all lengths or k=1/2 halving them, with sequences typically involving dilate by k from a center then rotate, reflect, or translate as needed to position, where dilation creates the size difference and others adjust position or orientation. For example, a triangle with sides 3-4-5 is similar to one with sides 6-8-10, checking proportionality: 6/3=8/4=10/5=2 for equal ratios with scale factor k=2, and a sequence could be dilate by 2 from the origin giving a similar triangle twice as large, then translate or rotate to match position if needed. In this case, the rectangles are not similar because the ratios of corresponding sides 2/3 ≠ 4/5, so no consistent scale factor exists, making choice C correct. Common errors include assuming all rectangles are similar like in A, using addition instead of ratios like in B, or believing only squares can be similar rectangles in D, confusing the need for proportional sides. To check similarity, identify corresponding sides such as shorter to shorter and longer to longer, calculate ratios 2/3 and 4/5, verify they are not equal, and note angles are all 90° but proportionality fails. Congruence is similarity with k=1 as a special case of same size and shape, and mistakes include claiming proportional when ratios differ or forgetting to check all pairs.
Rectangle $R$ is $2$ units by $4$ units. Rectangle $S$ is $3$ units by $5$ units. Are the rectangles similar?
Yes, all rectangles are similar.
No, because dilations always change angle measures.
No, because the side-length ratios are not equal: $\tfrac{2}{3} \ne \tfrac{4}{5}$.
Yes, because you can translate one rectangle onto the other.
Explanation
This question tests understanding of similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures have the same shape with proportional sides (corresponding sides have equal ratios forming scale factor k) and equal corresponding angles; it requires dilation since rigid transformations (rotation, reflection, translation) preserve size giving congruence (k=1), while dilation scales by factor k creating different sizes (k=2 doubles all lengths, k=1/2 halves); the sequence is typically 'dilate by k from center, then rotate/reflect/translate as needed to position' or variations—dilation creates size difference, others adjust position/orientation. For example, a triangle with sides 3-4-5 is similar to a triangle with sides 6-8-10; check proportionality: 6/3=8/4=10/5=2 (equal ratios, scale factor k=2), sequence could be 'dilate by 2 from origin' giving similar triangle 2× larger, then translate/rotate to match position if needed. The rectangles are not similar because side ratios are not equal: 2/3 ≠ 4/5 (or checking pairs: width 2 to 3 is 3/2, length 4 to 5 is 5/4, unequal), so choice C is correct. A common error is claiming all rectangles are similar, but only if proportions match (like squares), or thinking translations make them similar without dilation for size change. To check similarity: (1) measure corresponding sides (assume width 2 to 3, length 4 to 5), (2) calculate ratios (3/2=1.5, 5/4=1.25), (3) verify equal (no, not similar), (4) angles are all 90° but sides not proportional. Mistakes include claiming proportional when ratios differ or thinking dilations change angles, which they don't.
Triangle $LMN$ has vertices $L(2,1)$, $M(5,1)$, and $N(2,4)$. Triangle $L'M'N'$ has vertices $L'(-4,-2)$, $M'(-10,-2)$, and $N'(-4,-8)$. Which sequence of transformations maps $\triangle LMN$ to $\triangle L'M'N'$?
Dilate by scale factor $-2$ about the origin (a dilation with reflection), then translate left 0 and down 0 (no translation)
Dilate by scale factor $2$ about the origin, then translate left 8 and down 4
Dilate by scale factor $-2$ about the origin (a dilation with reflection), then translate left 0 and down 0
Translate left 6 and down 3 only (no dilation needed)
Explanation
This question tests understanding of similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures have the same shape with proportional sides where corresponding sides have equal ratios forming scale factor k, and equal corresponding angles; it requires dilation because rigid transformations like rotation, reflection, and translation preserve size giving congruence with k=1, while dilation scales by factor k creating different sizes, such as k=2 doubling all lengths or k=1/2 halving them, with sequences typically involving dilate by k from a center then rotate, reflect, or translate as needed to position, where dilation creates the size difference and others adjust position or orientation. For example, a triangle with sides 3-4-5 is similar to one with sides 6-8-10, checking proportionality: 6/3=8/4=10/5=2 for equal ratios with scale factor k=2, and a sequence could be dilate by 2 from the origin giving a similar triangle twice as large, then translate or rotate to match position if needed. Here, dilating by scale factor -2 about the origin (which includes a reflection) maps L(2,1) to (-4,-2), M(5,1) to (-10,-2), and N(2,4) to (-4,-8), exactly matching with no translation, so choice C is correct. A common error is using positive k without reflection or adding unnecessary translation like in A, or omitting dilation in D. To check, identify scale factor |k|=2 from side ratios and note the orientation flip indicating negative k, then verify coordinates match after transformation. Mistakes include forgetting the reflection aspect of negative k or trying rigid transformations only for size changes.
Triangle $ABC$ has side lengths $3,5,6$. Triangle $DEF$ has side lengths $3,4,5$. Are the triangles similar?
No, because dilation changes angles
No, because the ratios of corresponding sides are not all equal
Yes, because you can always translate one triangle to match the other
Yes, because each triangle has three sides
Explanation
This question tests understanding of similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures have the same shape with proportional sides where corresponding sides have equal ratios forming scale factor k, and equal corresponding angles; it requires dilation because rigid transformations like rotation, reflection, and translation preserve size giving congruence with k=1, while dilation scales by factor k creating different sizes, such as k=2 doubling all lengths or k=1/2 halving them, with sequences typically involving dilate by k from a center then rotate, reflect, or translate as needed to position, where dilation creates the size difference and others adjust position or orientation. For example, a triangle with sides 3-4-5 is similar to one with sides 6-8-10, checking proportionality: 6/3=8/4=10/5=2 for equal ratios with scale factor k=2, and a sequence could be dilate by 2 from the origin giving a similar triangle twice as large, then translate or rotate to match position if needed. In this case, the triangles are not similar because ratios like 3/3=1, 5/4=1.25, 6/5=1.2 are not equal, so no consistent k, making choice C correct. Common errors include assuming all triangles are similar like in A or B, or wrongly stating dilation changes angles in D, but dilation preserves angles. To check, calculate ratios of corresponding sides assuming possible orders, verify if all equal, and if not, they are not similar. Mistakes include not checking all ratios or confusing similarity with having the same number of sides.
Triangle $PQR$ has vertices $P(1,0)$, $Q(3,0)$, and $R(1,2)$. Triangle $P'Q'R'$ has vertices $P'(-2,1)$, $Q'(4,1)$, and $R'(-2,7)$. Which sequence of transformations maps $\triangle PQR$ to $\triangle P'Q'R'$?
Rotate $180^\circ$ about the origin, then translate left 3 and up 1
Translate left 3 and up 1, then dilate by scale factor $3$ about the origin
Translate left 5 and up 1 only (no dilation needed)
Dilate by scale factor $3$ about the origin, then translate left 5 and up 1
Explanation
This question tests understanding of similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures have the same shape with proportional sides where corresponding sides have equal ratios forming scale factor k, and equal corresponding angles; it requires dilation because rigid transformations like rotation, reflection, and translation preserve size giving congruence with k=1, while dilation scales by factor k creating different sizes, such as k=2 doubling all lengths or k=1/2 halving them, with sequences typically involving dilate by k from a center then rotate, reflect, or translate as needed to position, where dilation creates the size difference and others adjust position or orientation. For example, a triangle with sides 3-4-5 is similar to one with sides 6-8-10, checking proportionality: 6/3=8/4=10/5=2 for equal ratios with scale factor k=2, and a sequence could be dilate by 2 from the origin giving a similar triangle twice as large, then translate or rotate to match position if needed. Here, dilating by scale factor 3 about the origin followed by translating left 5 and up 1 maps PQR to P'Q'R', as dilation takes (1,0) to (3,0) then to (-2,1), and similarly for others, so choice B is correct. A common error is misordering transformations like translating first in A, which scales the translation incorrectly, or using only rigid transformations without dilation in D, impossible for size change. To find the sequence, identify scale factor from side ratios like base 2 to 6 giving k=3, describe dilation by 3 from origin, then add translation by comparing dilated points to targets. Mistakes include forgetting dilation for different sizes or using wrong translation vectors.
On a coordinate plane, triangle $ABC$ has points $A(1,1)$, $B(3,1)$, and $C(2,3)$. Triangle $A'B'C'$ has points $A'(-2,-2)$, $B'(-6,-2)$, and $C'(-4,-6)$. Which sequence of transformations maps $\triangle ABC$ to $\triangle A'B'C'$?
Translate by $(-3,-3)$, then rotate $90^\circ$ clockwise about the origin.
Dilate by scale factor $\tfrac{1}{2}$ about the origin, then translate by $(-4,-4)$.
Dilate by scale factor $2$ about the origin, then translate by $(-4,-4)$.
Reflect across the $y$-axis, then translate by $(-3,-3)$.
Explanation
This question tests understanding of similarity obtained via transformations including dilation—same shape, different sizes means proportional sides with scale factor k≠1. Similar figures have the same shape with proportional sides (corresponding sides have equal ratios forming scale factor k) and equal corresponding angles; it requires dilation since rigid transformations (rotation, reflection, translation) preserve size giving congruence (k=1), while dilation scales by factor k creating different sizes (k=2 doubles all lengths, k=1/2 halves); the sequence is typically 'dilate by k from center, then rotate/reflect/translate as needed to position' or variations—dilation creates size difference, others adjust position/orientation. For example, a triangle with sides 3-4-5 is similar to a triangle with sides 6-8-10; check proportionality: 6/3=8/4=10/5=2 (equal ratios, scale factor k=2), sequence could be 'dilate by 2 from origin' giving similar triangle 2× larger, then translate/rotate to match position if needed. The correct sequence is dilate by scale factor 2 about the origin (e.g., A(1,1) to (2,2), but then translate by (-4,-4) to (-2,-2); similarly for others), making choice B correct. A common error is using only rigid transformations for different sizes, which is impossible, or wrong scale factor like 1/2. To check similarity: (1) measure corresponding sides (e.g., AB distance $sqrt((3-1)^2$$+(1-1)^2$)=2, A'B' $sqrt((-6+2)^2$$+(-2+2)^2$)=4, ratio 4/2=2), (2) calculate ratios (all 2), (3) verify equal (yes, k=2), (4) angles equal as shapes match. Transformation sequence: identify k=2, dilate by 2 from origin, then translate by (-4,-4); mistakes include forgetting dilation or inverting k.