It is important to know that the transformation rule for a reflection across y = -x is
[tex](x,y)\rightarrow(-y,-x)[/tex]The transformation rule for a reflection across the x-axis is
[tex](x,y)\rightarrow(x,-y)[/tex]So, if we combine both rules, we get the following
[tex](x,y)\rightarrow(-y,-x)\rightarrow(-y,x)[/tex]This rule belongs to a counter-clockwise 90° rotation about the origin.
