21041中２・式の計算・計算問題・単項式の乗法1

$\begin{eqnarray}(1)\quad\;\;8x \times 4y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&8 \times 4 \times x \times y\\[5pt]&=&32xy\end{eqnarray}\;\;$

答$32xy$

$\begin{eqnarray}(2)\quad\;\;3a \times (\,-6b\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&3 \times (\,-6\,) \times a \times b\\[5pt]&=&-18ab\end{eqnarray}\;\;$

答$-18ab$

$\begin{eqnarray}(3)\quad\;\;(\,-4x\,) \times (\,-2yz\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-4 \times (\,-2\,) \times x \times yz\\[5pt]&=&8xyz\end{eqnarray}\;\;$

答$8xyz$

$\begin{eqnarray}(4)\quad\;\;12ab \times \dfrac{3}{\,4\,}c\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&\color{red}\cancelto{3}{\color{black}12} \color{black}\times \dfrac{3}{\,\color{red}\cancelto{1}{\color{black}4}\,} \times ab \times c\\[6pt]&=&9abc\end{eqnarray}\;\;$

答$9abc$

$\begin{eqnarray}(5)\quad\;\;\Bigl(\,-\dfrac{2}{\,3\,}xy\,\Bigr) \times 24z\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-\dfrac{2}{\,\color{red}\cancelto{1}{\color{black}3}\,} \times \color{red}\cancelto{8}{\color{black}24}\, \color{black}\times xy \times z\\[6pt]&=&-16xyz\end{eqnarray}\;\;$

答$-16xyz$

$\begin{eqnarray}(6)\quad\;\;\dfrac{4}{\,5\,}a \times \Bigl(\,-\dfrac{5}{\,12\,}\,\Bigr)bc\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&\dfrac{\,\color{red}\cancelto{1}{\color{black}4}\,}{\,\color{blue}\cancelto{1}{\color{black}5}\,} \times \Bigl(\,-\dfrac{\,\color{blue}\cancelto{1}{\color{black}5}\,}{\,\color{red}\cancelto{3}{\color{black}12}\,}\,\Bigr) \times a \times bc\\[6pt]&=&-\dfrac{1}{\,3\,}abc\end{eqnarray}\;\;$

答$-\dfrac{1}{\,3\,}abc$