The equation of the line of the mirror line
To describe a reflection on a grid, the equation of the mirror line is needed.
Example
Reflect the shape in the line \(x = -1\).
The line \(x = -1\) is a vertical line which passes through -1 on the \(x\)-axis.
Question
Describe the transformation of the shape ABC.
The line \(y = 1\) is a horizontal line which passes through 1 on the \(y\)-axis.
The shape has been reflected in the line \(y = 1\).
Question
Reflect the shape in the line \(y = x\).
The equation of a straight line graph has the form \(y = mx + c\), where \(m\) is the gradient and \(c\) is where the line crosses the \(y\)-axis.
The line \(y = x\) has a gradient of 1 and crosses the \(y\)-axis at (0,0).
Question
Describe the transformation of the shape ABC.
The mirror line has a gradient of -1 and crosses the \(y\)-axis at (0,0).
The shape has been reflected in the line \(y = -x\).
