Symmetry in Regular Polygons and Triangles

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Questions and Answers

If the smallest angle of rotation for a regular polygon is 18°, how many sides does the polygon have?

20

Which set of side lengths represents a triangle with 3 lines of reflectional symmetry?

5, 5, 5

Which figure shows a line of reflectional symmetry for the letter T?

Figure C

What is the order of rotational symmetry for a rhombus?

<p>2</p> Signup and view all the answers

A regular polygon has 15 sides. What is a possible angle of rotational symmetry for the figure?

<p>72°</p> Signup and view all the answers

How many lines of reflectional symmetry does an equilateral triangle have?

<p>3</p> Signup and view all the answers

Which triangle has 0 reflectional symmetries?

<p>triangle 1</p> Signup and view all the answers

Which letter in the word HAPPY has an order 2 rotational symmetry?

<p>H</p> Signup and view all the answers

Which statements are true about the lines of symmetry of a regular pentagon? Check all that apply.

<p>Every line bisects a vertex angle. (A), Every line bisects a side. (B), Every line is perpendicular to a side. (C)</p> Signup and view all the answers

Which figure has an order 3 rotational symmetry?

<p>equilateral triangle</p> Signup and view all the answers

What is the smallest angle of rotational symmetry for a square?

<p>90°</p> Signup and view all the answers

How can a regular hexagon be folded to show that it has reflectional symmetry?

<p>Fold the hexagon along a line that bisects two vertex angles.</p> Signup and view all the answers

If a quadrilateral has exactly 2 lines of symmetry, and both are angle bisectors, which statement would be true?

<p>The figure must be a rhombus because it has exactly 2 pairs of congruent angles.</p> Signup and view all the answers

Which figure has the same order of rotational symmetry as a rectangle?

<p>rhombus</p> Signup and view all the answers

Which type of triangle will always have exactly 1-fold reflectional symmetry?

<p>isosceles triangle</p> Signup and view all the answers

Which angle of rotation is an angle of rotational symmetry for all figures?

<p>360°</p> Signup and view all the answers

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Study Notes

Regular Polygon Symmetry

  • A regular polygon with a smallest angle of rotation of 18° has 20 sides.
  • A regular polygon with 15 sides has a rotational symmetry angle of 72°.
  • The smallest angle of rotational symmetry for a square is 90°.

Reflectional Symmetry in Triangles

  • An equilateral triangle has 3 lines of reflectional symmetry.
  • A triangle with side lengths of 5, 5, and 5 shows 3 lines of reflectional symmetry, making it an equilateral triangle.
  • An isosceles triangle has exactly 1 line of reflectional symmetry.

Rotational Symmetry

  • A rhombus has an order of rotational symmetry of 2.
  • An equilateral triangle possesses order 3 rotational symmetry.
  • The letter H in "HAPPY" features order 2 rotational symmetry.
  • A rhombus shares the same order of rotational symmetry as a rectangle.

Lines of Symmetry

  • A regular pentagon has multiple lines of symmetry: each bisects a vertex angle and a side, and is perpendicular to a side.
  • A quadrilateral with exactly 2 lines of symmetry, both being angle bisectors, is a rhombus due to its congruent angles.

Reflectional Symmetry in Letters

  • The letter T has a line of reflectional symmetry indicated in Figure C.

General Symmetry Facts

  • An angle of rotational symmetry applicable to all figures is 360°.

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