a)
[tex]12^{2} +x^{2} =20^{2}\\x^{2}=20^{2}-12^{2}\\x^{2}=400-144=256\\x=16[/tex]
[tex]12^{2}+5^{2}=x^{2} \\x^{2}=144+25=169\\x=13[/tex]
[tex]Ob= 20+13+16+5=54\\P=\frac{(16+5)*12}{2} = 126[/tex]
b)
[tex]6^{2} +x^{2} =6\sqrt{2}^{2} \\x^{2} =6\sqrt{2}^{2}- 6^{2} \\x^{2} =72-36=36\\x=6[/tex]
[tex]6^{2} +(2+6)^{2} = x^{2} \\x^{2} = 36+64=100\\x=10[/tex]
[tex]Ob=2+10+6\sqrt{2}= 12+6\sqrt{2}\\P= \frac{2*6}{2} =6[/tex]
