Bài 2:
\(A=\sqrt{14+6\sqrt{5}}-\sqrt{8-2\sqrt{15}}\\ =\sqrt{\left(3+\sqrt{5}\right)^2}-\sqrt{\left(\sqrt{5}-\sqrt{3}\right)^2}\\ =3+\sqrt{5}-\sqrt{5}+\sqrt{3}=3+\sqrt{3}\)
b. \(A=\sqrt{7-2\sqrt{10}}-\sqrt{7+2\sqrt{10}}\\ =\sqrt{\left(\sqrt{5}-\sqrt{2}\right)^2}-\sqrt{\left(\sqrt{5}+\sqrt{2}\right)^2}\\ =\sqrt{5}-\sqrt{2}-\sqrt{5}-\sqrt{2}=-2\sqrt{2}\)
15: \(\left(\sqrt{28}-2\sqrt{3}+\sqrt{7}\right)\cdot\sqrt{7}+\sqrt{84}\)
\(=\left(2\sqrt{7}+\sqrt{7}-2\sqrt{3}\right)\cdot\sqrt{7}+2\sqrt{21}\)
\(=63-2\sqrt{21}+2\sqrt{21}=63\)
16: \(\left(\sqrt{28}-2\sqrt{14}+\sqrt{7}\right)\cdot\sqrt{7}+7\sqrt{8}\)
\(=\left(2\sqrt{7}+\sqrt{7}-2\sqrt{14}\right)\cdot\sqrt{7}+7\cdot2\sqrt{2}\)
\(=\left(3\sqrt{7}-2\sqrt{14}\right)\cdot\sqrt{7}+14\sqrt{2}\)
\(=21-2\sqrt{98}+14\sqrt{2}=21-14\sqrt{2}+14\sqrt{2}=21\)
17: \(\left(\sqrt{12}-2\sqrt{18}+5\sqrt{3}\right)\cdot\sqrt{3}+5\sqrt{6}\)
\(=\left(2\sqrt{3}-2\cdot3\sqrt{2}+5\sqrt{3}\right)\cdot\sqrt{3}+5\sqrt{6}\)
\(=\left(7\sqrt{3}-6\sqrt{2}\right)\cdot\sqrt{3}+5\sqrt{6}\)
\(=21-6\sqrt{6}+5\sqrt{6}=21-\sqrt{6}\)
18: \(\left(\sqrt{99}-\sqrt{18}-\sqrt{11}\right)\cdot\sqrt{11}+3\sqrt{22}\)
\(=\left(3\sqrt{11}-3\sqrt{2}-\sqrt{11}\right)\cdot\sqrt{11}+3\sqrt{22}\)
\(=2\sqrt{11}\cdot\sqrt{11}-3\sqrt{22}+3\sqrt{22}\)
=22
