Đáp án:
\(\begin{array}{l}
a)14\sqrt 2 \\
d) - 1\\
b)9\\
e)\dfrac{{24 + \sqrt 5 }}{2}\\
c) - 5a
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
a)3\sqrt 2 - 5.2\sqrt 2 + 7.3\sqrt 2 \\
= \left( {3 - 10 + 21} \right)\sqrt 2 \\
= 14\sqrt 2 \\
d)\sqrt {5 - 2.2.\sqrt 5 + 4} - \sqrt {5 - 2.\sqrt 5 .1 + 1} \\
= \sqrt {{{\left( {\sqrt 5 - 2} \right)}^2}} - \sqrt {{{\left( {\sqrt 5 - 1} \right)}^2}} \\
= \sqrt 5 - 2 - \left( {\sqrt 5 - 1} \right)\\
= \sqrt 5 - 2 - \sqrt 5 + 1\\
= - 1\\
b)3 - 4 + 2.5 = 9\\
e)\dfrac{{{{\left( {\sqrt 7 + \sqrt 5 } \right)}^2} + {{\left( {\sqrt 7 - \sqrt 5 } \right)}^2}}}{{7 - 5}} + \sqrt {\dfrac{5}{4}} \\
= \dfrac{{12 + 2\sqrt {35} + 12 - 2\sqrt {32} }}{2} + \dfrac{{\sqrt 5 }}{2}\\
= \dfrac{{24 + \sqrt 5 }}{2}\\
c)3\left| a \right| - 2a = - 3a - 2a = - 5a
\end{array}\)
