Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
Chapter Review
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Exercise 11 Page 223

When a point with coordinates (x,y) is rotated 180^(∘) counterclockwise about the origin, the coordinates of its image are (- x,- y).

Practice makes perfect

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.