Big Ideas Math: Modeling Real Life, Grade 8
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Big Ideas Math: Modeling Real Life, Grade 8 View details
3. Rotations
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Exercise 17 Page 61

When a point with coordinates (x,y) is rotated 270^(∘) counterclockwise about the origin, the coordinates of its image are (y,- x).

W'(- 2,6), X'(- 2,2), Y'(- 6,2), Z'(- 6,5)

Practice makes perfect

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 clockwise 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 rotate a quadrilateral 270^(∘) counterclockwise about the origin. A rotation by 270^(∘) counterclockwise ends up in the same place as a rotation by 90^(∘) clockwise. Therefore, we can use the coordinate changes shown in the table that correspond to a 90^(∘) clockwise to determine the coordinates of the image of each vertex. ccc Preimage & & Image (x,y) & → & (y,- x) [0.5em] W(- 6,-2) & & W'(- 2,6) [0.5em] X(- 2,- 2) & & X'(- 2,2) [0.5em] Y(- 2,- 6) & & Y'(-6,2) [0.5em] Z(- 5,- 6) & & Z'(- 6,5) We can now plot the obtained points and draw the image of the given quadrilateral after the rotation!
preimage and image

Extra

Visualizing the Rotation
Let's rotate WXYZ 270^(∘) counterclockwise about the origin so that we can see how it is mapped onto W'X'Y'Z'.
rotate