One transformation being followed by another is described as a single transformation. When a shape is reflected on one line and then on another line, this creates more than one transformation. However, the original shape can be transformed though the second line in one step.
For example: in the following perpendicular mirror lines:
Shape A in mirror line m1 produces shape A’ which in turn produces shape A” though the m2 mirror line.
To combine the transformations into one step, the reflection of the shape is equal to a single transformation of 180º
Rotations can also be combined into a single step though the same centre. In the example below, A can be mapped to A” through a rotation of 270° clockwise or 90° anti-clockwise.
Translation are combine though reviewing the steps of the first and second translation. For example, in the diagram below, A becomes into A” in a single step by translating 5 units left and two units down.