21091中２・式の計算・計算問題・かっこをふくむ式1

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

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

$\begin{eqnarray}\quad\;\;&=&2x-5y+3x + 12y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&2x +3x -5y + 12y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&5x + 7y\end{eqnarray}\;\;$

答$5x + 7y$

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

$\begin{eqnarray}\quad\;\;&=&-5a+b-2 \times 3a -2 \times b\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-5a+b-6a -2b\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-5a-6a+b -2b\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-11a-b\end{eqnarray}\;\;$

答$-11a-b$

$\begin{eqnarray}(3)\quad\;\;4(\,6x-3y\,)+5(\,-5x+2y\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&4 \times 6x +4 \times (\,-3y\,)+5 \times (\,-5x\,) +5 \times 2y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&24x -12y -25x +10y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&24x -25x -12y +10y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-x-2y\end{eqnarray}\;\;$

答$-x-2y$

$\begin{eqnarray}(4)\quad\;\;7(\,4a-b\,)-9(\,2a-4b\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&7 \times 4a +7 \times (\,-b\,)-9 \times 2a -9 \times (\,4b\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&28a -7b -18a +36b\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&28a -18a -7b +36b \end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&10a + 29b\end{eqnarray}\;\;$

答$10a + 29b$

$\begin{eqnarray}(5)\quad\;\;-6(\,-3x+2y\,)-8(\,-2x-3y\,)\end{eqnarray}\;\;$

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

$\begin{eqnarray}\quad\;\;&=&18x-12y+16x+24y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&18x+16x-12y+24y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&34x+12y\end{eqnarray}\;\;$

答$34x+12y$