2. Упростите: а) \(\sqrt{2a}-2\sqrt{18a}+\sqrt{72a}\); б) \(\sqrt{5a}-3\sqrt{20a}+\sqrt{125a}\); в) \(4\sqrt2+\sqrt{50}-\sqrt{18}\); г) \(\frac12\sqrt{12}-2\sqrt{27}+\sqrt{45}\); д) \(\frac13\sqrt{18}+3\sqrt8-\sqrt{98}\); е) \(2\sqrt5(\sqrt{20}-3\sqrt5)\); ж) \(\sqrt{11+2\sqrt5}\cdot\sqrt{11-2\sqrt5}\).

1. \(\sqrt{2a}-2\sqrt{18a}+\sqrt{72a}=\sqrt{2a}-6\sqrt{2a}+6\sqrt{2a}=\sqrt{2a}\).
2. \(\sqrt{5a}-3\sqrt{20a}+\sqrt{125a}=\sqrt{5a}-6\sqrt{5a}+5\sqrt{5a}=0\).
3. \(4\sqrt2+\sqrt{50}-\sqrt{18}=4\sqrt2+5\sqrt2-3\sqrt2=6\sqrt2\).
4. \(\frac12\sqrt{12}-2\sqrt{27}+\sqrt{45}=\sqrt3-6\sqrt3+3\sqrt5=3\sqrt5-5\sqrt3\).
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. \(\sqrt{11+2\sqrt5}\cdot\sqrt{11-2\sqrt5}=\sqrt{(11+2\sqrt5)(11-2\sqrt5)}=\sqrt{121-20}=\sqrt{101}\).

Ответ: а) \(\sqrt{2a}\); б) 0; в) \(6\sqrt2\); г) \(3\sqrt5-5\sqrt3\); д) 0; е) −10; ж) \(\sqrt{101}\).