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8th grade · Math · Unit 11 of 17

Congruent Shapes

Slides, flips and turns that keep a shape the same

What your child practices

Recognizing congruent shapes, matching corresponding sides and angles, and finding the coordinates of a point after a slide, flip or turn.

Alabama Course of Study content standard: 8.24 · congruent figures and the rigid motions that map one onto the other

How we explain it

Children can open this short lesson before they practice.

  1. Congruent shapes have the same size and shape.
  2. Slides, flips and turns keep a shape congruent.
  3. Matching sides and angles are equal.

Example: A triangle is slid across the page. Is the new triangle congruent? A slide does not change size or shape. So the triangles match. Answer: Yes

Congruent Shapes in Alabama

In the Alabama Course of Study, this is unit 11 of 17 in 8th grade Math, after Equations with Brackets and before Exponent Rules.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Alabama State Department of Education (ALSDE)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Polygon ABCD is congruent to polygon PQRS, with A matching P, B matching Q and so on. If AB = 5 cm, which side must also be 5 cm?

    • RS
    • QR
    • SP
    • PQ

  2. Question 2

    A 4 cm by 6 cm rectangle and a 6 cm by 4 cm rectangle are…

    • congruent
    • not congruent, because 4 ≠ 6
    • not congruent, because they point different ways
    • similar but never congruent

  3. Question 3

    Point A(7, 3) is rotated 180° about the origin. What are the coordinates of A′?

    • (7, -3)
    • (3, 7)
    • (-7, -3)
    • (-7, 3)

  4. Question 4

    Two triangles have sides 3 cm, 4 cm, 5 cm and 3 cm, 4 cm, 6 cm. Are they congruent?

    • yes, they are both triangles
    • yes, two sides match
    • only if their angles are 90°
    • no, one pair of sides is different

  5. Question 5

    In congruent polygons, matching angles and sides are called…

    • corresponding
    • parallel
    • opposite
    • adjacent

  6. Question 6

    Point A(-5, 1) is translated 3 units right and 3 units down. What are the coordinates of A′?

    • (-2, 4)
    • (-8, 4)
    • (-2, -2)
    • (-8, -2)

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