[tex]\bf \sqrt{13^2-5^2} =\sqrt{169-25} =\sqrt{144}=12[/tex]
[tex]\bf\sqrt{12^2+16^2} =\sqrt{144+256} =\sqrt{400} =20[/tex]
[tex]\bf \sqrt{2 \cdot 3^2+7 \cdot 3^2} = \sqrt{3^2(2+7)} = \sqrt{9 \cdot 9 } =9[/tex]
[tex]\bf \sqrt{9 \cdot 5^2-8\cdot 5^2} = \sqrt{5^2(9-8)} =\sqrt{5^2} =5[/tex]
