Resposta :
[tex]\sqrt{20} - \sqrt{45} + 3\sqrt{125} \\\\ Fatorando... \\\\ 20 \ | \div 2 \\ 10 \ | \div 2 \\ 5 \ \ | \div 5 \\ 1 \\\\ \sqrt{20} = \sqrt{2^{2} \cdot 5} = \underline{2\sqrt{5}}[/tex]
[tex]45 \ | \div 5 \\ 9 \ \ | \div 3 \\ 3 \ \ | \div 3 \\ 1 \\\\ \sqrt{45} = \sqrt{3^{2} \cdot 5} = \underline{3\sqrt{5}}[/tex]
[tex]125 \ | \div 5 \\ 25 \ \ | \div 5 \\ 5 \ \ \ | \div 5 \\ 1 \\\\ 3\sqrt{125}= 3\sqrt{5^{2} \cdot 5} = 3 \cdot 5\sqrt{5} = \underline{15\sqrt{5}}[/tex]
[tex]2\sqrt{5} - 3\sqrt{5} + 15\sqrt{5} = \boxed{14\sqrt{5}}[/tex]