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When a point with coordinates (x,y) is rotated 180^(∘) counterclockwise about the origin, the coordinates of its image are (- x,- y).
Let's start by graphing the polygon with vertices W(-2,- 1), X(-1,3), Y(3,3), and Z(3,- 3).
A rotation is a transformation about a fixed point called center of rotation. Each point of the original figure and its image are the same distance from the center of rotation. When a counterclockwise rotation is performed about the origin, the coordinates of the image can be written in relation to the coordinates of the preimage.
| Rotations About the Origin | ||
|---|---|---|
| 90^(∘) Rotation | 180^(∘) Rotation | 270^(∘) Rotation |
|
ccc Preimage & & Image [0.5em] (x,y) & → & (- y,x) |
ccc Preimage & & Image [0.5em] (x,y) & → & (- x,- y) |
ccc Preimage & & Image [0.5em] (x,y) & → & (y,- x) |
We want to graph the image of the given polygon after a 180^(∘) counterclockwise rotation about the origin. To do so, we can use the information in the above table to find the coordinates of the image of each vertex.
| Point | (x,y) | (- x,- y) |
|---|---|---|
| W | (- 2,- 1) | (2,1) |
| X | (- 1,3) | (1,- 3) |
| Y | (3,3) | (- 3,- 3) |
| Z | (3,- 3) | (- 3,3) |
Now that we know the vertices of the rotated figure, we can draw it.