Envision Math 2.0: Grade 8, Volume 2
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4. Compose Transformations
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Exercise 13 Page 320

Practice makes perfect
We are asked to determine which figure is the image of Figure A after a reflection across the x-axis and a translation 4 units right.

To reflect Figure A, we need to reflect all its vertices. To do so, we will map them to the other side of the line of reflection — the x-axis. Note that the reflected points will be the same distance from the line of reflection as the original points, but will be located on its other side. Let's do it!

Now, let's translate Figure A' 4 units to the right.

weird

We found that the image is Figure E. This result corresponds with answer D.

We want to determine which figure can be transformed into G after the following sequence of transformations.

Transformation
1. Rotation 90^(∘) about the origin
2. Translation 13 units right
3. Translation 4 units down

To find which figure was transformed into G, we can apply the inverse of each transformation to G.

Transformation Inverse
1. Rotation 90^(∘) about the origin 1. Rotation -90 ^(∘) about the origin
2. Translation 13 units right 2. Translation 13 units left
3. Translation 4 units down 3. Translation 4 units up
We will apply these transformations to G in reverse order.

Transformations
3. Translation 4 units up
2. Translation 13 units left
1. Rotation -90 ^(∘) about the origin

We will translate Figure G 4 units up, 13 units left, and then rotate it -90^(∘), which is equal to 270^(∘), about the origin. Let's start with the translation.

weird

Now, we will rotate FigureG 270^(∘) about the origin. Recall that to perform a rotation we need to change the x- and y-coordinates of the points of the rectangle as shown in the following table.

Angle of Rotation Rule
90^(∘) (x,y)→ (- y,x)
180^(∘) (x,y)→ (- x,- y)
270 ^(∘) (x,y)→ (y,- x)

We want to rotate FigureG 270^(∘) around the origin. Let's change the coordinates of each vertex of the translated Figure G. ccc (x,y) & → & ( y, - x) [0.5em] (-7,-2) & → & (-2,7) [0.5em] (-4,-2) & → & (-2,4) [0.5em] (-4,-5) & → & (-5,4) [0.5em] (-6,-5) & → & (-5,6) [0.5em] (-7,-3) & → & (-3,7) Let's graph the figure after rotation!

weird

After applying the inverse of each given transformation to Figure G we got Figure B. Therefore, Figure B can be transformed into G after the given transformations! This result corresponds with answer A.

Checking Our Answer

Transforming B Into G
Let's apply the given transformations to Figure B. First, we will rotate it 90^(∘) about the origin.

weird

Next, let's translate it 13 units right and 4 units down.

weird

We found that the Figure B can be transformed into G using the given transformations.