quy đồng mẫu thức các phân thức sau a) X/16,xy/20 (b)1/4x,3/6y (c) xy/8 , y/15 d) x/2y,y/2x (e) xy/8, yz/12,xz/24 (f) xy/2z,yz/12,zx/4y

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1. Đáp án:

   $\begin{array}{l}
   a)\dfrac{x}{{16}};\dfrac{{xy}}{{20}}\\
   MSC = 80\\
    \Rightarrow \left\{ \begin{array}{l}
   \dfrac{x}{{16}} = \dfrac{{x.5}}{{16.5}} = \dfrac{{5x}}{{80}}\\
   \dfrac{{xy}}{{20}} = \dfrac{{xy.4}}{{20.4}} = \dfrac{{4xy}}{{80}}
   \end{array} \right.\\
   b)\dfrac{1}{{4x}};\dfrac{3}{{6y}} = \dfrac{1}{{2y}}\\
   MSC = 4xy\\
    \Rightarrow \left\{ \begin{array}{l}
   \dfrac{1}{{4x}} = \dfrac{y}{{4xy}}\\
   \dfrac{3}{{6y}} = \dfrac{1}{{2y}} = \dfrac{{2x}}{{4xy}}
   \end{array} \right.\\
   c)\dfrac{{xy}}{8};\dfrac{y}{{15}}\\
    \Rightarrow MSC = 120\\
    \Rightarrow \left\{ \begin{array}{l}
   \dfrac{{xy}}{8} = \dfrac{{15xy}}{{120}}\\
   \dfrac{y}{{15}} = \dfrac{{8y}}{{120}}
   \end{array} \right.\\
   d)\dfrac{x}{{2y}};\dfrac{y}{{2x}}\\
    \Rightarrow MSC = 2xy\\
    \Rightarrow \left\{ \begin{array}{l}
   \dfrac{x}{{2y}} = \dfrac{{{x^2}}}{{2xy}}\\
   \dfrac{y}{{2x}} = \dfrac{{{y^2}}}{{2xy}}
   \end{array} \right.\\
   e)\dfrac{{xy}}{8};\dfrac{{yz}}{{12}};\dfrac{{xz}}{{24}}\\
    \Rightarrow MSC = 48\\
    \Rightarrow \left\{ \begin{array}{l}
   \dfrac{{xy}}{8} = \dfrac{{6xy}}{{48}}\\
   \dfrac{{yz}}{{12}} = \dfrac{{4yz}}{{48}}\\
   \dfrac{{xz}}{{24}} = \dfrac{{2xz}}{{48}}
   \end{array} \right.\\
   f)\dfrac{{xy}}{{2z}};\dfrac{{yz}}{{12}};\dfrac{{xz}}{{4y}}\\
    \Rightarrow MSC = 12yz\\
    \Rightarrow \left\{ \begin{array}{l}
   \dfrac{{xy}}{{2z}} = \dfrac{{6x{y^2}}}{{12yz}}\\
   \dfrac{{yz}}{{12}} = \dfrac{{{y^2}{z^2}}}{{12yz}}\\
   \dfrac{{zx}}{{4y}} = \dfrac{{3{z^2}x}}{{12yz}}
   \end{array} \right.
   \end{array}$

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