Big Ideas Math: Modeling Real Life, Grade 8
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Big Ideas Math: Modeling Real Life, Grade 8 View details
2. Reflections
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Exercise 3 Page 51

Practice makes perfect

Let's start by plotting the given points and connecting them to draw our rectangle.

polygon

To reflect this figure over the x-axis, we need to plot each vertex of the image A'B'C'D' the same distance from the line of reflection as its vertex on the preimage ABCD. Because our line of reflection is the x-axis, this will change the sign of the y-coordinates of the points, but the x-coordinates will remain unchanged.

Preimage ABCD Image A'B'C'D'
Vertex Distance From the x-axis Vertex Distance From the x-axis
A(- 4,- 3) 3 units below the x-axis A'(- 4,3) 3 units above the x-axis
B(-4,-1) 1 unit below the x-axis B'(-4,1) 1 unit above the x-axis
C(- 1,- 1) 1 unit below the x-axis C'(- 1,1) 1 unit above the x-axis
D(- 1,- 3) 3 units below the x-axis D'(- 1,3) 3 units above the x-axis
Let's do the reflection!
translation

Let's draw again our rectangle.

polygon

This time we want to reflect this figure over the y-axis. This will change the sign of the x-coordinates of the points, but the y-coordinates will remain unchanged.

Preimage ABCD Image A'B'C'D'
Vertex Distance From the y-axis Vertex Distance From the y-axis
A(- 4,- 3) 4 units to the left of the y-axis A'( 4,-3) 4 units to the right of the y-axis
B(-4,-1) 4 units to the left of the y-axis B'(4,-1) 4 units to the right of the y-axis
C(- 1,- 1) 1 unit to the left of the y-axis C'( 1,-1) 1 unit to the right of the y-axis
D(- 1,- 3) 1 unit to the left of the y-axis D'( 1,-3) 1 unit to the right of the y-axis
Now, we can apply the reflection!
translation