21092中２・式の計算・計算問題・かっこをふくむ式2

$\begin{eqnarray}(1)\quad\;\;x-2y+3(\,4x+5y\,)-4(\,-3x+2y\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&x-2y+3 \times 4x+3 \times 5y -4 \times (\,-3x\,) -4 \times 2y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&x-2y+12x+15y +12x -8y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&x+12x+12x-2y+15y -8y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&25x +5y\end{eqnarray}\;\;$

答$25x +5y$

$\begin{eqnarray}(2)\quad\;\;4(\,2a-4b+6c\,)-3(\,3a-5b+7c\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&4 \times 2a +4 \times (\,-4b\,) +4 \times 6c -3 \times 3a -3 \times (\,-5b\,) -3 \times 7c\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&8a -16b +24c -9a +15b -21c\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&8a -9a -16b +15b+24c -21c\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-a -b +3c\end{eqnarray}\;\;$

答$-a -b +3c$

$\begin{eqnarray}(3)\quad\;\;9(\,3x-y\,)-2(\,-6x+8y\,)+6(\,-6x+7y\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&9 \times 3x +9 \times (\,-y\,) -2 \times (\,-6x\,) -2 \times 8y +6 \times (\,-6x\,) +6 \times 7y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&27x -9y +12x -16y -36x +42y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&27x +12x -36x -9y -16y +42y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&3x+17y\end{eqnarray}\;\;$

答$3x+17y$

$\begin{eqnarray}(4)\quad\;\;7(\,4a^{2}-2a\,)-(\,5a^{2}-4a+5\,)-5(\,4a^{2}-5a-2\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&7 \times 4a^{2} +7 \times (\,-2a\,) - 5a^{2}+4a-5 -5 \times 4a^{2} -5 \times (\,-5a\,) -5 \times (\,-2\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&28a^{2} -14a - 5a^{2}+4a-5 -20a^{2} +25a +10\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&28a^{2} - 5a^{2} - 20a^{2} -14a + 4a +25a -5 +10\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&3a^{2} +15a +5\end{eqnarray}\;\;$

答$3a^{2} +15a +5$