Rotating Triangles 180 Degrees Around the Origin

🔑 Key Concepts

  • A \(180^\circ\) rotation is a half-turn around the origin.
  • The coordinate rule is \((x,y)\rightarrow(-x,-y)\).
  • Both coordinates change signs, but the order of the coordinates stays the same.
  • A \(180^\circ\) rotation is a rigid transformation.

💡 Main Idea

To rotate a triangle \(180^\circ\) around the origin, make each coordinate its opposite. Points in Quadrant I move to Quadrant III, and points in Quadrant III move to Quadrant I.

✏️ Worked Example

🧠 Math Vocabulary

  • Rotation: a transformation that turns a figure around a fixed point.
  • \(180^\circ\) Rotation: a half-turn around the center of rotation.
  • Origin: the point \((0,0)\), where the \(x\)-axis and \(y\)-axis intersect.
  • Center of Rotation: the fixed point around which a figure turns.
  • Rigid Transformation: a transformation that keeps the same size and shape.
  • Image: the new figure after a transformation.
  • Preimage: the original figure before a transformation.
  • Coordinate Rule: an algebraic rule that shows how ordered pairs change during a transformation.

📚 What You Should Already Know

Students should know how to plot ordered pairs, identify the origin, name the four quadrants, and find opposites of positive and negative numbers.

🚀 What Comes Next

Next, students can compare \(180^\circ\) rotations with \(90^\circ\) clockwise and counterclockwise rotations around the origin.

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