Step by step
The question
Question: reflect the shape A(2, 1), B(4, 1) and C(4, 3) in the y-axis.
1 Draw the shape
Put the points on the grid and join them.
2 Draw the mirror line
The mirror line is the y-axis.
Reflecting flips the shape over the line, like a mirror.
Each point lands just as far away, on the other side.
3 Reflect each point
From A, count straight to the mirror line: 2.
Then count 2 more on the other side.
We call the new point A prime.
The little mark means: the new A.
A is 2 right of the y-axis.
Its image is 2 left of it.
Its y stays 1.
So A' is (−2, 1).
Careful!
The y-axis goes up and down.
The flip goes left or right, so x changes.
y stays.
B is 4 right of it, so B' is 4 left of: (−4, 1).
C is 4 right of it, so C' is 4 left of: (−4, 3).
4 Draw the image
Join the new points.
This new shape is called the image.
So the image is A'(−2, 1), B'(−4, 1) and C'(−4, 3).
5 Check
Let's check with the rule for the y-axis: x changes sign, y stays the same.
It gives the same points.
Right!
Let's look back.
First: draw the shape.
Then: draw the mirror line.
Then: reflect each point.
Then: draw the image.
Last: check.