Step by step
The question
Question: glide reflect the shape A(−3, 1), B(−1, 1) and C(−1, 3): reflect in the line x = 1, then translate down 2.
1 Draw the shape
Put the points on the grid and join them.
The mirror line is the line x = 1.
A glide reflection is a slide along the mirror line, and a flip in it.
Like footprints in the sand: left, right, left.
Careful!
The mirror line is upright.
So the slide goes up or down, along it.
Any other slide is not a glide.
2 Flip
Flip in the line x = 1: count from the point to the line, then the same again on the other side.
A is (−3, 1): it goes to (5, 1).
B goes to (3, 1).
C goes to (3, 3).
Join them.
3 Slide
Down 2: y gets 2 smaller.
The rule: (x, y − 2).
A' is (5, 1): it goes to (5, −1).
B' goes to (3, −1).
C' goes to (3, 1).
Join them: the final image.
So the image is A''(5, −1), B''(3, −1) and C''(3, 1).
4 Check
Let's check the other way round: slide first, then flip.
For a glide, it must give the same points.
The same points as before.
Right!
Let's look back.
First: draw the shape.
Then: flip.
Then: slide.
Last: check.