Bonsoir,
Je suppose que c'est ceci : "On donne x = V72 et y=V98"
1) [tex]x=\sqrt{72}\\x=\sqrt{36\times2}\\x=\sqrt{36}\times\sqrt{2}\\x=6\sqrt{2}\\\\y=\sqrt{98}\\y=\sqrt{49\times2}\\y=\sqrt{49}\times\sqrt{2}\\y=7\sqrt{2}[/tex]
2) [tex]x^2-y^2=(\sqrt{72})^2-(\sqrt{98})^2\\\\x^2-y^2=72-98\\\\x^2-y^2=-26[/tex]
[tex]x+y=6\sqrt{2}+7\sqrt{2}\\\\x+y=13\sqrt{2}[/tex]