21042中２・式の計算・計算問題・単項式の乗法2

$\begin{eqnarray}(1)\quad\;\;3x \times 7x\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&3 \times 7 \times x \times x\\[5pt]&=&21x^{2}\end{eqnarray}\;\;$

答$21x^{2}$

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

$\begin{eqnarray}\quad\;\;&=&2 \times (\,-6\,) \times a \times a^{2}\\[5pt]&=&-12a^{3}\end{eqnarray}\;\;$

答$-12a^{3}$

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

$\begin{eqnarray}\quad\;\;&=&-4 \times (\,-2\,) \times x^{2} \times x \times y\\[5pt]&=&8x^{3}y\end{eqnarray}\;\;$

答$8x^{3}y$

$\begin{eqnarray}(4)\quad\;\;6ab \times 5abc\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&6 \times 5 \times a \times a \times b \times b \times c\\[5pt]&=&30a^{2}b^{2}c\end{eqnarray}\;\;$

答$30a^{2}b^{2}c$

$\begin{eqnarray}(5)\quad\;\;(\,-2xy\,) \times 4x^{2}y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-2 \times 4 \times x \times x^{2} \times y \times y\\[5pt]&=&-8x^{3}y^{2}\end{eqnarray}\;\;$

答$-8x^{3}y^{2}$

$\begin{eqnarray}(6)\quad\;\;(\,-8abc\,) \times ab^{2}c^{2}\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-8 \times a \times a \times b \times b^{2} \times c \times c^{2} \\[6pt]&=&-8a^{2}b^{3}c^{3}\end{eqnarray}\;\;$

答$-8a^{2}b^{3}c^{3}$