Step by step
The question
Question: glide reflect the shape A(1, 3), B(3, 3) and C(1, 5): translate right 3, then reflect in the line y = 1.
1 Draw the shape
Put the points on the grid and join them.
The mirror line is the line y = 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 flat.
So the slide goes left or right, along it.
Any other slide is not a glide.
2 Slide
Right 3: x gets 3 bigger.
The rule: (x + 3, y).
A is (1, 3): it goes to (4, 3).
B goes to (6, 3).
C goes to (4, 5).
Join them.
3 Flip
Flip in the line y = 1: count from the point to the line, then the same again on the other side.
A' is (4, 3): it goes to (4, −1).
B' goes to (6, −1).
C' goes to (4, −3).
Join them: the final image.
So the image is A''(4, −1), B''(6, −1) and C''(4, −3).
4 Check
Let's check the other way round: flip first, then slide.
For a glide, it must give the same points.
The same points as before.
Right!
Let's look back.
First: draw the shape.
Then: slide.
Then: flip.
Last: check.