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9th grade · Math · Unit 10 of 18

Line & Rotation Symmetry

Fold lines, turns and the order of symmetry.

What your child practices

Practices lines of symmetry and rotation symmetry (order and angle of rotation) in polygons, letters and designs.

Alabama Course of Study content standard: GDA.22 · line and rotation symmetry: the reflections and turns that carry a figure onto itself

How we explain it

Children can open this short lesson before they practice.

  1. Line symmetry: a fold makes both halves match.
  2. Rotation symmetry: the shape fits on itself after a partial turn.
  3. The order is how many times it fits in one full turn.

Example: A square is turned about its center. How many times does it fit in a full turn? It fits every 90°. 360 ÷ 90 = 4. Answer: 4

Line & Rotation Symmetry in Alabama

In the Alabama Course of Study, this is unit 10 of 18 in 9th grade Math, after Circle Properties and before Surface Area of Objects.

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

    What is the order of rotation symmetry of a rectangle that is not a square?

    • 4
    • 1
    • 2

  2. Question 2

    How many lines of symmetry does a rectangle that is not a square have?

    • 4
    • 2
    • 1

  3. Question 3

    What is the smallest turn angle for a regular octagon?

    • 90°
    • 45°
    • 60°

  4. Question 4

    How many lines of symmetry does an equilateral triangle have?

    • 6
    • 3
    • 1

  5. Question 5

    How many lines of symmetry does a scalene triangle have?

    • 3
    • 0
    • 1

  6. Question 6

    A pattern has rotation symmetry with a smallest angle of 40°. What is its order?

    • 4
    • 9
    • 40

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