ANSWER:
[tex](x,y)\rightarrow(y,-x)\text{ or }(x,y)\rightarrow(-y,x)[/tex]STEP-BY-STEP EXPLANATION:
When they are rotated 90 ° they can be clockwise or counterclockwise, each one has a specific rule, they are the following:
[tex]\begin{gathered} \text{ Clockwise} \\ (x,y)\rightarrow(y,-x) \\ \text{ Counterclockwise} \\ (x,y)\rightarrow(-y,x) \end{gathered}[/tex]