TEKS Math 8.3.B
The Standard
compare and contrast the attributes of a shape and its dilation(s) on a coordinate plane
Texas Essential Knowledge and Skills for Mathematics
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students examine an original figure and a dilated image on a coordinate plane. They identify which measurements stay the same and which change according to the scale factor.
What Mastery Looks Like
- Students correctly identify equal corresponding angles, proportional side lengths, and parallel corresponding sides. They calculate how side lengths, perimeter, and area change under a given scale factor.
Common Misconceptions
- Students may think a dilation changes angle measures or makes a different kind of shape. They may add the scale factor to side lengths, or forget that area changes by the square of the scale factor.
How to Assess It
- Give students a triangle and its dilation on a coordinate grid. Ask them to list two attributes that stay the same and two that change, with measurements as evidence.
Lesson moves
Ways to Teach It
Have students trace a polygon on grid paper, dilate it from a marked center, then measure corresponding sides and angles.
Ask students to explain why a dilation creates a similar figure but usually not a congruent figure.
Play a matching game with cards showing original figures, dilated figures, scale factors, and attribute statements.
Use a phone photo resized to 150 percent, then compare its dimensions, perimeter, area, angles, and overall shape.
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Printable 8.3.B Worksheet
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Related Standards
- K.6.D
identify attributes of two-dimensional shapes using informal and formal geometric language interchangeably
- 8.3.C
use an algebraic representation to explain the effect of a given positive rational scale factor applied to two-dimensional figures on a coordinate plane with th...
- 8.10.A
generalize the properties of orientation and congruence of rotations, reflections, translations, and dilations of two-dimensional shapes on a coordinate plane
- 8.3.A
generalize that the ratio of corresponding sides of similar shapes are proportional, including a shape and its dilation
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