Question

Difficulty: MediumTransformations in the Coordinate Plane

In the standard (x,y)(x, y) coordinate plane, rectangle ABCDABCD has vertices A(−3,1)A(-3, 1), B(−1,1)B(-1, 1), C(−1,4)C(-1, 4), and D(−3,4)D(-3, 4). The rectangle is first reflected across the yy-axis and then translated 33 units to the left and 22 units down. What are the coordinates of the final image of vertex CC?

  1. (−2,2)(-2, 2)Answer
  2. B
    (4,2)(4, 2)
  3. C
    (−2,6)(-2, 6)
  4. D
    (−4,−6)(-4, -6)
  5. E
    (−4,2)(-4, 2)

Answer

(−2,2)(-2, 2)
To find the final image of vertex C(−1,4)C(-1, 4), we first apply the reflection across the yy-axis. The rule for reflecting a point across the yy-axis is (x,y)→(−x,y)(x, y) \rightarrow (-x, y). Applying this to C(−1,4)C(-1, 4) gives C′(1,4)C'(1, 4). Next, we apply the translation of 33 units to the left and 22 units down. The rule for this translation is (x,y)→(x−3,y−2)(x, y) \rightarrow (x - 3, y - 2). Applying this to C′(1,4)C'(1, 4) gives C′′(1−3,4−2)=(−2,2)C''(1 - 3, 4 - 2) = (-2, 2).

Step-by-Step Solution

1
Identify the initial coordinates of vertex CC.
C(−1,4)C(-1, 4)
We need to find the final image of vertex CC, so we start with its given coordinates.
2
Apply the reflection across the yy-axis to vertex CC.
C′(1,4)C'(1, 4)
Reflecting a point (x,y)(x, y) across the yy-axis negates the x-coordinate, changing (x,y)(x, y) to (−x,y)(-x, y).
3
Apply the translation of 33 units to the left and 22 units down to the reflected point C′C'.
C′′(−2,2)C''(-2, 2)
Translating a point (x,y)(x, y) by 33 units to the left subtracts 33 from the x-coordinate (x−3x - 3), and translating 22 units down subtracts 22 from the y-coordinate (y−2y - 2).

Key Concept

Composite transformations in the coordinate plane involve applying multiple geometric transformations in a specific sequence.
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