Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
3. Rotations
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Exercise 11 Page 194

A 90^(∘) rotation counterclockwise about the origin will change the coordinates of the endpoints such that (a,b)→ (- b,a).

Practice makes perfect

Let's consider each of the transformations one at a time, beginning with the translation.

Translation

Translations tell us how many units we should add to or subtract from the given coordinates. Let's look at the given translation. (x,y) → (x,y + 2) This means that we should move each endpoint of XY 2 units up.

From the diagram, we can determine the coordinates of the image. X'(- 3,3) and Y'(4,- 3)

Rotation

When a segment is rotated 90^(∘) counterclockwise about the origin, the coordinates of the image's endpoints will change in the following way. (a,b) → (- b,a) Using this rule with the endpoints of X'Y', we can find the endpoints of X''Y''.

Point (a,b) (- b,a)
X' (- 3,3) (- 3,- 3)
Y' (4,- 3) (3,4)

Knowing the endpoints of X''Y'', we can draw the image.

Final Image

The final image X''Y'' will be the segment resulting from the translation followed by the rotation.