Reflection and Translation on a Grid
Identify, describe, and represent the position of a shape following a reflection or translation using appropriate language; know that the shape has not changed
What a learner can do afterwards
- Reflect a triangle in a vertical mirror line on a coordinate grid and state the new coordinates
- Translate a shape 3 units right and 2 units up and describe the movement
- Explain that a reflected/translated shape is congruent to the original
1 · Read
You already know how to flip a shape over a line and how to slide it across a grid. Now you will do both of these on a coordinate grid, and describe the shape's new position using coordinates.
Triangle ABC has corners at (2, 1), (5, 1), and (3, 4). Reflect it in the vertical line x = 0. Each y-coordinate stays the same, but each x-coordinate flips sign: A' (-2, 1), B' (-5, 1), C' (-3, 4).
A square's corner starts at (1, 2). It slides 3 units right and 2 units up. Add 3 to the x-coordinate and 2 to the y-coordinate: (1 + 3, 2 + 2) = (4, 4).
After a reflection or a translation, the shape is congruent to the original. Congruent means exactly the same size, with the same angles, just sitting in a new spot on the grid. Nothing stretches, shrinks, or bends. Only the position changes.
Reflecting or translating a shape only changes its position on the grid. The shape itself, its size and its angles, never change.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.