The transformation is a reflection in the line 
followed by a reflection in the line 
.
The mapping for a reflection in the line is 
.
That is simply swapping the coordinates.
Now we reflect the resulting coordinates in the line which has the mapping 
So we transform the resulting coordinates as follows:
Hence we have
The mapping for a reflection in the line
That is simply swapping the coordinates.
Now we reflect the resulting coordinates in the line
So we transform the resulting coordinates as follows:
Hence we have