Step by step
The question
Question: glide reflect the shape A(0, 4), B(2, 4) and C(0, 2): translate right 2, then reflect in the line y = 3.
1 Draw the shape
Put the points on the grid and join them.
The mirror line is the line y = 3.
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 2: x gets 2 bigger.
The rule: (x + 2, y).
A is (0, 4): it goes to (2, 4).
B goes to (4, 4).
C goes to (2, 2).
Join them.
3 Flip
Flip in the line y = 3: count from the point to the line, then the same again on the other side.
A' is (2, 4): it goes to (2, 2).
B' goes to (4, 2).
C' goes to (2, 4).
Join them: the final image.
So the image is A''(2, 2), B''(4, 2) and C''(2, 4).
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.