[tex]AB= \sqrt{(X _{B}-X _{A}) ^{2} +(Y _{B}-Y _{A}) ^{2} } [/tex]
[tex]AB= \sqrt{(5-1) ^{2}+(2-2) ^{2} } =\ \textgreater \ AB=4 cm[/tex]
[tex]BC= \sqrt{(3-5) ^{2}+(-1-2) ^{2} } = \sqrt{4+9} =\ \textgreater \ BC= \sqrt{13} cm[/tex]
[tex]AC= \sqrt{(3-1) ^{2}+(-1-2) ^{2} } = \sqrt{4+9} =\ \textgreater \ AC= \sqrt{13} cm[/tex]
Perim.=4+2√13
=2(2+√13) cm