13.
[tex]x^{2} +5^{2} =7^{2} \\x^{2} +25=49/-25\\x^{2} =24\\x=2\sqrt{6} \\b)\\2^{2} +x^{2} =5^{2} \\4+x^{2} =25/-4\\x^{2} =21\\x=\sqrt{21} \\(\sqrt{21}) ^{2} +6^{2} =y^{2} \\21+36=y^{2} \\y=\sqrt{57} \\c)\\5^{2} +x^{2} =15^{2}\\25+x^{2} =225/-25\\x^{2} =200\\x=10\sqrt{2} \\5^{2} +y^{2} =13^{2} \\25+y^{2} =169/-25\\y^{2} =144\\y=12\\x-y=z\\10\sqrt{2}-12=z\\z=-12+10\sqrt{2}[/tex]
