Giải thích các bước giải:
$\begin{array}{l}
17.\sqrt {{{\left( {\sqrt 2 - 1} \right)}^2}} = \left| {\sqrt 2 - 1} \right| = \sqrt 2 - 1\\
18.\sqrt {{{\left( {2 - \sqrt 5 } \right)}^2}} = \left| {2 - \sqrt 5 } \right| = \sqrt 5 - 2\\
19.\sqrt {{{\left( {2 - \sqrt 3 } \right)}^2}} = \left| {2 - \sqrt 3 } \right| = 2 - \sqrt 3 \\
20.\sqrt {{{\left( {3 - \sqrt {11} } \right)}^2}} = \left| {3 - \sqrt {11} } \right| = \sqrt {11} - 3\\
21.\sqrt {{{\left( {4 + \sqrt 2 } \right)}^2}} = \left| {4 + \sqrt 2 } \right| = 4 + \sqrt 2 \\
22.\sqrt {{{\left( {3 - \sqrt 3 } \right)}^2}} = \left| {3 - \sqrt 3 } \right| = 3 - \sqrt 3 \\
23.\sqrt {{{\left( {4 - \sqrt {17} } \right)}^2}} = \left| {4 - \sqrt {17} } \right| = \sqrt {17} - 4\\
24.\sqrt {{{\left( {5 - \sqrt {29} } \right)}^2}} = \left| {5 - \sqrt {29} } \right| = \sqrt {29} - 5\\
25.\sqrt {{{\left( {1 - \sqrt 2 } \right)}^2}} = \left| {1 - \sqrt 2 } \right| = \sqrt 2 - 1\\
26.\sqrt {{{\left( {\sqrt 6 - \sqrt 7 } \right)}^2}} = \left| {\sqrt 6 - \sqrt 7 } \right| = \sqrt 7 - \sqrt 6 \\
27.2\sqrt 3 + \sqrt {{{\left( {2 - \sqrt 3 } \right)}^2}} = 2\sqrt 3 + 2 - \sqrt 3 = 2 + \sqrt 3 \\
28.\sqrt {{{\left( {7 + \sqrt 3 } \right)}^2}} + \sqrt {{{\left( {2 - \sqrt 3 } \right)}^2}} = \left| {7 + \sqrt 3 } \right| + \left| {2 - \sqrt 3 } \right| = 7 + \sqrt 3 + 2 - \sqrt 3 = 9\\
29.\sqrt {{{\left( {\sqrt 5 + 1} \right)}^2}} + \sqrt {{{\left( {\sqrt 5 - 1} \right)}^2}} = \left| {\sqrt 5 + 1} \right| + \left| {\sqrt 5 - 1} \right| = \sqrt 5 + 1 + \sqrt 5 - 1 = 2\sqrt 5 \\
30.\sqrt {{{\left( {2 - \sqrt 5 } \right)}^2}} - \sqrt {{{\left( {3 - \sqrt 5 } \right)}^2}} = \left| {2 - \sqrt 5 } \right| - \left| {3 - \sqrt 5 } \right| = \sqrt 5 - 2 - 3 + \sqrt 5 = \sqrt 5 - 5\\
31.\sqrt {{{\left( {\sqrt 7 - 4} \right)}^2}} - \sqrt {28} = \left| {\sqrt 7 - 4} \right| - 2\sqrt 7 = 4 - \sqrt 7 - 2\sqrt 7 = 4 - 3\sqrt 7 \\
32.\sqrt {{{\left( {3 + \sqrt 2 } \right)}^2}} + \sqrt {{{\left( {3 - \sqrt 2 } \right)}^2}} = \left| {3 + \sqrt 2 } \right| + \left| {3 - \sqrt 2 } \right| = 3 + \sqrt 2 + 3 - \sqrt 2 = 6\\
33.\sqrt {{{\left( {\sqrt 3 - 2} \right)}^2}} + \sqrt {{{\left( {\sqrt 3 - 1} \right)}^2}} = \left| {\sqrt 3 - 2} \right| + \left| {\sqrt 3 - 1} \right| = 2 - \sqrt 3 + \sqrt 3 - 1 = 1\\
34.4\sqrt 5 + 2\sqrt {{{\left( {\sqrt 5 - 7} \right)}^2}} = 4\sqrt 5 + 2\left| {\sqrt 5 - 7} \right| = 4\sqrt 5 + 2\left( {7 - \sqrt 5 } \right) = 14 + 2\sqrt 5 \\
35.\sqrt {20} + 2\sqrt {{{\left( {\sqrt 5 - 2} \right)}^2}} = 2\sqrt 5 + 2\left| {\sqrt 5 - 2} \right| = 2\sqrt 5 + 2\left( {\sqrt 5 - 2} \right) = 4\sqrt 5 - 4
\end{array}$
