201 How are translations and reflections represented as a function? What is the relationship between translations, reflections, and rigid motion? How do rigid motions affect a given figure? 202 How are rotations represented as a function? What is the relationship between a rotation and a rigid motion? How can a sequence of transformations map a figure onto itself? 203 How do you connect the ideas of congruency and rigid motion? How does the criteria for triangle congruence (ASA, SAS, AAS, and SSS) follow from the definition of congruence in terms of rigid motions? What does it mean for two shapes to be congruent? How do you prove that a point on a perpendicular bisector is equidistant from the endpoints of the segment it intersects? 204 How do you prove each of the following theorems using either a two-column, paragraph, or flow-chart proof? Triangle Sum Theorem, Triangle Inequality Theorem, Isosceles Triangle Theorem, Converse of the Isosceles Triangle Theorem How do you use theorems about triangles to solve problems? 205 How do you prove each of the following theorems using either a two-column, paragraph, or flow-chart proof? Midsegment of a Triangle Theorem, Concurrency of Medians Theorem How do you use theorems about triangles to solve problems? 206 What are the characteristics of squares, rhombi, kites, and trapezoids? How do you prove each of the properties of a parallelogram? How do you use theorems about parallelograms to solve problems? 207-Honors ONLY How do you identify and draw lines of symmetry? How do you identify rotational symmetry and angles of rotation? How do you construct a proof by contradiction?

1 answer

These questions cover a wide range of geometric concepts related to transformations, congruence, theorems, and figures. Here’s an organized response addressing each of your queries:

201. Translations and Reflections

  • Representing Translations and Reflections as Functions:

    • A translation can be represented as a function \( T(x, y) = (x + a, y + b) \), where \( (a, b) \) are the horizontal and vertical shifts, respectively.
    • A reflection can be represented by functions like \( R_y(x, y) = (-x, y) \) for a reflection over the y-axis, or \( R_x(x, y) = (x, -y) \) for a reflection over the x-axis.
  • Relationship with Rigid Motion:

    • Both translations and reflections are types of rigid motions, meaning they preserve distance and angles. Consequently, the shape and size of a figure remain unchanged.
    • Rigid motions include translations, reflections, and rotations.
  • Effect on a Given Figure:

    • Rigid motions move figures without altering their shape, size, or position in terms of congruency. A shape and its image after a rigid motion are congruent.

202. Rotations

  • Representing Rotations as Functions:

    • A rotation around the origin by an angle \( \theta \) can be represented as \( R(x, y) = (x \cos \theta - y \sin \theta, x \sin \theta + y \cos \theta) \).
  • Relationship with Rigid Motion:

    • Rotations are also rigid motions. They preserve the size and shape of figures while altering their orientation.
  • Mapping a Figure onto Itself:

    • A figure can be rotated to map onto itself if there exists an angle of rotation for which the image coincides with the original figure. This is common in shapes with rotational symmetry.

203. Congruency and Rigid Motion

  • Connection Between Congruency and Rigid Motion:

    • Two shapes are congruent if one can be obtained from the other through a series of rigid motions. This means that all corresponding sides and angles are equal.
  • Triangle Congruence Criteria:

    • The criteria ASA (Angle-Side-Angle), SAS (Side-Angle-Side), AAS (Angle-Angle-Side), and SSS (Side-Side-Side) follow from the definition of congruence: they ensure that corresponding sides and angles of triangles are equal via rigid motions.
  • Equidistance from a Perpendicular Bisector:

    • To prove that any point on a perpendicular bisector is equidistant from the endpoints, consider points \( A \) and \( B \) as endpoints of a segment. If point \( P \) lies on the perpendicular bisector, then triangles \( APB \) and \( BAP \) are congruent (by the definition of bisector and right angles). Therefore, \( PA = PB \).

204. Triangle Theorems

  • Proving Triangle Theorems:

    • Use a structured approach (two-column, paragraph, or flow-chart proofs) to show:
      • Triangle Sum Theorem: The sum of the interior angles in a triangle is 180°.
      • Triangle Inequality Theorem: The sum of lengths of two sides must be greater than the length of the third side.
      • Isosceles Triangle Theorem: If two sides are equal, the angles opposite them are equal.
      • Converse: If two angles in a triangle are equal, the sides opposite them are equal.
  • Using Theorems in Problem Solving:

    • Apply these theorems to find unknown angle measures or side lengths in various geometric problems involving triangles.

205. More Triangle Theorems

  • Proving theorems like the Midsegment of a Triangle and Concurrency of Medians can follow similar proof strategies as previously mentioned:
    • Midsegment Theorem: The segment connecting the midpoints of two sides of a triangle is parallel to the third side and half its length.
    • Concurrency of Medians: All three medians of a triangle intersect at a single point (the centroid).

206. Properties of Quadrilaterals

  • Characteristics of Special Quadrilaterals:

    • Squares: Four equal sides, four right angles, diagonals are equal and bisect each other at right angles.
    • Rhombi: Four equal sides, diagonals bisect each other, not necessarily equal.
    • Kites: Two pairs of equal adjacent sides, one pair of equal angles (between unequal sides), and diagonals intersect at a right angle.
    • Trapezoids: At least one pair of parallel sides; isosceles trapezoids have equal non-parallel sides and angles.
  • Proving Properties of Parallelograms:

    • Show using definitions and properties that opposite sides/angles are equal, and diagonals bisect each other.

207-Honors ONLY: Symmetry and Proof by Contradiction

  • Identifying Lines of Symmetry: Look for lines that divide a shape into two mirror images.
  • Rotational Symmetry: Identify shapes that can be rotated about a center point and coincide with their original position. Measure angles for the smallest rotation.
  • Constructing Proof by Contradiction: Assume the opposite of what you want to prove, and demonstrate that this leads to a contradiction.

This summary provides an overview of the concepts and techniques related to transformations, congruency, and specific geometric theorems as requested.