Đáp án:
\(\begin{array}{l}
17)\sqrt 5 + \sqrt 3 + 1\\
18)\sqrt 2 \\
19)1 - x\\
20) - 2\sqrt b
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
17)\left| {\sqrt 5 + 2} \right| + \sqrt {3 - 2\sqrt 3 .1 + 1} \\
= \sqrt 5 + 2 + \sqrt {{{\left( {\sqrt 3 - 1} \right)}^2}} \\
= \sqrt 5 + 2 + \sqrt 3 - 1\\
= \sqrt 5 + \sqrt 3 + 1\\
18)\dfrac{{7\left( {\sqrt 3 + \sqrt 2 } \right)}}{{3 - 2}} - 7\sqrt 3 - 2.3\sqrt 2 \\
= 7\sqrt 3 + 7\sqrt 2 - 7\sqrt 3 - 6\sqrt 2 \\
= \sqrt 2 \\
19)\left( {1 + \dfrac{{\sqrt x \left( {\sqrt x + 1} \right)}}{{\sqrt x + 1}}} \right).\left( {1 - \dfrac{{\sqrt 2 \left( {\sqrt x - 1} \right)}}{{\sqrt x - 1}}} \right)\\
= \left( {1 + \sqrt x } \right)\left( {1 - \sqrt x } \right)\\
= 1 - x\\
20)\dfrac{{\sqrt {ab} \left( {\sqrt a - \sqrt b } \right)}}{{\sqrt {ab} }} - \dfrac{{\left( {\sqrt a - \sqrt b } \right)\left( {\sqrt a + \sqrt b } \right)}}{{\sqrt a - \sqrt b }}\\
= \sqrt a - \sqrt b - \sqrt a - \sqrt b \\
= - 2\sqrt b
\end{array}\)
