Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
B = \dfrac{{x + y - 2\sqrt {xy} }}{{\sqrt x - \sqrt y }} - \dfrac{{x + \sqrt {xy} }}{{\sqrt x + \sqrt y }}\\
= \dfrac{{{{\left( {\sqrt x - \sqrt y } \right)}^2}}}{{\sqrt x - \sqrt y }} - \dfrac{{\sqrt x \left( {\sqrt x + \sqrt y } \right)}}{{\sqrt x + \sqrt y }}\\
= \left( {\sqrt x - \sqrt y } \right) - \sqrt x \\
= - \sqrt y \\
b,\\
y = 2018 - 2\sqrt {2017} = 2017 - 2.\sqrt {2017} .1 + 1 = {\left( {\sqrt {2017} - 1} \right)^2}\\
\Rightarrow \sqrt y = \sqrt {2017} - 1\\
E = A - \sqrt {2017} = - \sqrt y - \sqrt {2017} = - \sqrt {2017} + 1 - \sqrt {2017} = 1 - 2\sqrt {2017}
\end{array}\)
