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