2. Упростите: а) \(\sqrt{20}-2\sqrt{180}+\sqrt{72}\); б) \(\sqrt{50}-3\sqrt{80}+\sqrt{125}\); в) \(4\sqrt2+\sqrt{50}-\sqrt{18}\); г) \(\frac12\sqrt{12}-2\sqrt{27}+\sqrt{75}\); д) \(\frac13\sqrt{18}+3\sqrt8-\sqrt{98}\); е) \(2\sqrt5(\sqrt{20}-3\sqrt5)\); ж) \((\sqrt{11}+2\sqrt5)(\sqrt{11}-2\sqrt5)\).

1. \(\sqrt{20}-2\sqrt{180}+\sqrt{72}=2\sqrt5-12\sqrt5+6\sqrt2=-10\sqrt5+6\sqrt2\).
2. \(\sqrt{50}-3\sqrt{80}+\sqrt{125}=5\sqrt2-12\sqrt5+5\sqrt5=5\sqrt2-7\sqrt5\).
3. \(4\sqrt2+\sqrt{50}-\sqrt{18}=4\sqrt2+5\sqrt2-3\sqrt2=6\sqrt2\).
4. \(\frac12\sqrt{12}-2\sqrt{27}+\sqrt{75}=\sqrt3-6\sqrt3+5\sqrt3=0\).
5. \(\frac13\sqrt{18}+3\sqrt8-\sqrt{98}=\sqrt2+6\sqrt2-7\sqrt2=0\).
6. \(2\sqrt5(\sqrt{20}-3\sqrt5)=2\sqrt5(2\sqrt5-3\sqrt5)=-10\).
7. \((\sqrt{11}+2\sqrt5)(\sqrt{11}-2\sqrt5)=11-(2\sqrt5)^2=11-20=-9\).

Ответ: а) \(-10\sqrt5+6\sqrt2\); б) \(5\sqrt2-7\sqrt5\); в) \(6\sqrt2\); г) 0; д) 0; е) −10; ж) −9.