$\begin{eqnarray}(1)\;\;3x+2+6x-5&=&3x+6x+2-5\\[5pt]&=&(\,3+6\,)x-3\\[5pt]&=&9x-3\end{eqnarray}\;\;$

答$9x-3$

$\begin{eqnarray}(2)\;\;x-5y+3x-2y&=&x+3x-5y-2y\\[5pt]&=&(\,1+3\,)x+(\,-5-2\,)y\\[5pt]&=&4x-7y\end{eqnarray}\;\;$

答$4x-7y$

$\begin{eqnarray}(3)\quad\;\;6a-4b-5+5a-7b-1\end{eqnarray}\;\;$

$\quad\;\;\begin{eqnarray}&=&6a+5a-4b-7b-5-1\\[6pt]&=&11a-11b-6\end{eqnarray}\;\;$

答$11a-11b-6$

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

$\quad\;\;\begin{eqnarray}&=&-x^{2}+6x^{2}-4x+5x+3-2\\[6pt]&=&5x^{2}+x+1\end{eqnarray}\;\;$

答$5x^{2}+x+1$

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

$\quad\;\;\begin{eqnarray}&=&4a^{2}-5a^{2}-6ab+7ab+3b^{2}+2b^{2}\\[6pt]&=&-a^{2}+ab+5b^{2}\end{eqnarray}\;\;$

答$-a^{2}+ab+5b^{2}$

$\begin{eqnarray}(1)\quad\;\;2.4a-0.5-1.1b+1.2+0.7b-1.8a\end{eqnarray}\;\;$

$\quad\;\;\begin{eqnarray}&=&2.4a-1.8a-1.1b+0.7b-0.5+1.2\\[6pt]&=&0.6a-0.4b+0.7\end{eqnarray}\;\;$

答$0.6a-0.4b+0.7$

$\begin{eqnarray}(2)\quad\;\;-\dfrac{1}{\;2\;}x^{2}+\dfrac{1}{\;2\;}x-\dfrac{1}{\;2\;}-\dfrac{1}{\;3\;}x+\dfrac{1}{\;3\;}+\dfrac{1}{\;3\;}x^{2}\end{eqnarray}\;\;$

$\quad\;\;\begin{eqnarray}&=&-\dfrac{1}{\;2\;}x^{2}+\dfrac{1}{\;3\;}x^{2}+\dfrac{1}{\;2\;}x-\dfrac{1}{\;3\;}x-\dfrac{1}{\;2\;}+\dfrac{1}{\;3\;}\\[6pt]&=&-\dfrac{3}{\;6\;}x^{2}+\dfrac{2}{\;6\;}x^{2}+\dfrac{3}{\;6\;}x-\dfrac{2}{\;6\;}x-\dfrac{3}{\;6\;}+\dfrac{2}{\;6\;}\\[6pt]&=&-\dfrac{1}{\;6\;}x^{2}+\dfrac{1}{\;6\;}x-\dfrac{1}{\;6\;}\end{eqnarray}\;\;$

答$-\dfrac{1}{\;6\;}x^{2}+\dfrac{1}{\;6\;}x-\dfrac{1}{\;6\;}$

$\begin{eqnarray}(3)\quad\;\;200b^{2}-120ab+400a^{2}+320ab-500a^{2}+100b^{2}\end{eqnarray}\;\;$

$\quad\;\;\begin{eqnarray}&=&400a^{2}-500a^{2}-120ab+320ab+200b^{2}+100b^{2}\\[6pt]&=&-100a^{2}+200ab+300b^{2}\end{eqnarray}\;\;$

答$-100a^{2}+200ab+300b^{2}$

$\begin{eqnarray}(4)\quad\;\;-\dfrac{2}{\;5\;}x^{2}-4.5xy+\dfrac{3}{\;5\;}y^{2}-0.6y^{2}-\dfrac{1}{\;2\;}xy+2.4x^{2}\end{eqnarray}\;\;$

$\quad\;\;\begin{eqnarray}&=&-\dfrac{2}{\;5\;}x^{2}+2.4x^{2}-4.5xy-\dfrac{1}{\;2\;}xy+\dfrac{3}{\;5\;}y^{2}-0.6y^{2}\\[6pt]&=&-\dfrac{2}{\;5\;}x^{2}+\dfrac{\;12\;}{5}x^{2}-\dfrac{9}{\;2\;}xy-\dfrac{1}{\;2\;}xy+\dfrac{3}{\;5\;}y^{2}-\dfrac{3}{\;5\;}y^{2}\\[6pt]&=&\dfrac{\;10\;}{5}x^{2}-\dfrac{\;10\;}{\;2\;}xy+0\\[6pt]&=&2x^{2}-5xy\end{eqnarray}\;\;$

答$2x^{2}-5xy$

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

$\begin{eqnarray}\quad\;\;&=&x+3+x-2\\[5pt]&=&x+x+3-2\\[5pt]&=&2x+1\end{eqnarray}\;\;$

答$2x+1$

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

$\begin{eqnarray}\quad\;\;&=&3a+b+4a+6b\\[5pt]&=&3a+4a+b+6b\\[5pt]&=&7a+7b\end{eqnarray}\;\;$

答$7a+7b$

$\begin{eqnarray}(3)\quad\;\;(\,-4x^{2}-3xy\,)+(\,-7x^{2}+2xy\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-4x^{2}-3xy-7x^{2}+2xy\\[5pt]&=&-4x^{2}-7x^{2}-3xy+2xy\\[5pt]&=&-11x^{2}-xy\end{eqnarray}\;\;$

答$-11x^{2}-xy$

$\begin{eqnarray}(4)\quad\;\;(\,-2x-5y+9\,)+(\,x-7y-4\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-2x-5y+9+x-7y-4\\[5pt]&=&-2x+x-5y-7y+9-4\\[5pt]&=&-x-12y+5\end{eqnarray}\;\;$

答$-x-12y+5$

$\begin{eqnarray}(5)\quad\;\;(\,6a^{2}-4a-5\,)+(\,-5a^{2}-9a+7\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&6a^{2}-4a-5-5a^{2}-9a+7\\[5pt]&=&6a^{2}-5a^{2}-4a-9a-5+7\\[5pt]&=&a^{2}-13a+2\end{eqnarray}\;\;$

答$a^{2}-13a+2$

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

$\begin{eqnarray}\quad\;\;&=&2x^{2}+8xy-3y^{2}+6x^{2}-7xy-y^{2}\\[5pt]&=&2x^{2}+6x^{2}+8xy-7xy-3y^{2}-y^{2}\\[5pt]&=&8x^{2}+xy-4y^{2}\end{eqnarray}\;\;$

答$8x^{2}+xy-4y^{2}$

$\begin{eqnarray}(1)\quad\;\;(\,2.1x-0.3y+1.5\,)+(\,-1.2x-0.2y-0.6\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&2.1x-0.3y+1.5-1.2x-0.2y-0.6\\[5pt]&=&2.1x-1.2x-0.3y-0.2y+1.5-0.6\\[5pt]&=&0.9x-0.5y+0.9\end{eqnarray}\;\;$

答$0.9x-0.5y+0.9$

$\begin{eqnarray}(2)\quad\;\;\Bigl(\,-\dfrac{\;a^{2}\;}{\;5\;}-\dfrac{\;a\;}{\;3\;}-\dfrac{\;1\;}{\;4\;}\,\Bigr)+\Bigl(\,\dfrac{\;a^{2}\;}{\;2\;}+\dfrac{a}{\;5\;}+\dfrac{\;1\;}{\;3\;}\,\Bigr)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-\dfrac{\;a^{2}\;}{\;5\;}-\dfrac{\;a\;}{\;3\;}-\dfrac{\;1\;}{\;4\;}+\dfrac{\;a^{2}\;}{\;2\;}+\dfrac{a}{\;5\;}+\dfrac{\;1\;}{\;3\;}\\[6pt]&=&-\dfrac{\;a^{2}\;}{\;5\;}+\dfrac{\;a^{2}\;}{\;2\;}-\dfrac{\;a\;}{\;3\;}+\dfrac{a}{\;5\;}-\dfrac{\;1\;}{\;4\;}+\dfrac{\;1\;}{\;3\;}\\[6pt]&=&-\dfrac{\;2\;}{\;10\;}a^{2}+\dfrac{\;5\;}{\;10\;}a^{2}-\dfrac{\;5\;}{\;15\;}a+\dfrac{3}{\;15\;}a-\dfrac{\;3\;}{\;12\;}+\dfrac{\;4\;}{\;12\;}\\[6pt]&=&\dfrac{\;3\;}{\;10\;}a^{2}-\dfrac{\;2\;}{\;15\;}a+\dfrac{\;1\;}{\;12\;}\end{eqnarray}\;\;$

答$\dfrac{\;3\;}{\;10\;}a^{2}-\dfrac{\;2\;}{\;15\;}a+\dfrac{\;1\;}{\;12\;}$

$\begin{eqnarray}(3)\quad\;\;(\,0.01a^{2}+0.04ab-b^{2}\,)+(\,-0.03a^{2}+0.06ab-0.5b^{2}\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&0.01a^{2}+0.04ab-b^{2}-0.03a^{2}+0.06ab-0.5b^{2}\\[5pt]&=&0.01a^{2}-0.03a^{2}+0.04ab+0.06ab-b^{2}-0.5b^{2}\\[5pt]&=&-0.02a^{2}+0.1ab-1.5b^{2}\end{eqnarray}\;\;$

答$-0.02a^{2}+0.1ab-1.5b^{2}$

$\begin{eqnarray}(4)\quad\;\;\Bigl(\,3x^{2}-\dfrac{\;xy\;}{\;5\;}+3y^{2}\,\Bigr)+\Bigl(\,-\dfrac{2}{\;3\;}x^{2}+xy-\dfrac{\;y^{2}\;}{2}\,\Bigr)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&3x^{2}-\dfrac{\;xy\;}{\;5\;}+3y^{2}-\dfrac{2}{\;3\;}x^{2}+xy-\dfrac{\;y^{2}\;}{2}\\[6pt]&=&3x^{2}-\dfrac{2}{\;3\;}x^{2}-\dfrac{\;xy\;}{\;5\;}+xy+3y^{2}-\dfrac{\;y^{2}\;}{2}\\[6pt]&=&\dfrac{9}{\;3\;}x^{2}-\dfrac{2}{\;3\;}x^{2}-\dfrac{\;1\;}{\;5\;}xy+\dfrac{5}{\;5\;}xy+\dfrac{6}{\;2\;}y^{2}-\dfrac{\;1\;}{2}y^{2}\\[6pt]&=&\dfrac{7}{\;3\;}x^{2}+\dfrac{4}{\;5\;}xy+\dfrac{5}{\;2\;}y^{2}\end{eqnarray}\;\;$

答$\dfrac{7}{\;3\;}x^{2}+\dfrac{4}{\;5\;}xy+\dfrac{5}{\;2\;}y^{2}$

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

$\begin{eqnarray}\quad\;\;&=&x+5\color{red}-\color{black}x\color{red}-\color{black}4\\[5pt]&=&x-x+5-4\\[5pt]&=&1\end{eqnarray}\;\;$

答$1$

$\begin{eqnarray}(2)\quad\;\;(\,6a-b\,)-(\,5a-2b\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&6a-b\color{red}-\color{black}5a\color{red}+\color{black}2b\\[5pt]&=&6a-5a-b+2b\\[5pt]&=&a+b\end{eqnarray}\;\;$

答$a+b$

$\begin{eqnarray}(3)\quad\;\;(\,3x^{2}+7xy\,)-(\,-12x^{2}+8xy\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&3x^{2}+7xy\color{red}+\color{black}12x^{2}\color{red}-\color{black}8xy\\[5pt]&=&3x^{2}+12x^{2}+7xy-8xy\\[5pt]&=&15x^{2}-xy\end{eqnarray}\;\;$

答$15x^{2}-xy$

$\begin{eqnarray}(4)\quad\;\;(\,-9x-2y-1\,)-(\,9x-y+1\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-9x-2y-1\color{red}-\color{black}9x\color{red}+\color{black}y\color{red}-\color{black}1\,)\\[5pt]&=&-9x-9x-2y+y-1-1\\[5pt]&=&-18x-y-2\end{eqnarray}\;\;$

答$-18x-y-2$

$\begin{eqnarray}(5)\quad\;\;(\,8a^{2}+6a-9\,)-(\,-14a^{2}+5a-20\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&8a^{2}+6a-9\color{red}+\color{black}14a^{2}\color{red}-\color{black}5a\color{red}+\color{black}20\\[5pt]&=&8a^{2}+14a^{2}+6a-5a-9+20\\[5pt]&=&22a^{2}+a+11\end{eqnarray}\;\;$

答$22a^{2}+a+11$

$\begin{eqnarray}(6)\quad\;\;(\,15x^{2}-3xy+2y^{2}\,)-(\,25x^{2}-18xy-11y^{2}\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&15x^{2}-3xy+2y^{2}\color{red}-\color{black}25x^{2}\color{red}+\color{black}18xy\color{red}+\color{black}11y^{2}\\[5pt]&=&15x^{2}-25x^{2}-3xy+18xy+2y^{2}+11y^{2}\\[5pt]&=&-10x^{2}+15xy+13y^{2}\end{eqnarray}\;\;$

答$-10x^{2}+15xy+13y^{2}$

$\begin{eqnarray}(1)\quad\;\;(\,1.9x-0.4y-0.8\,)-(\,-0.8x-0.4y-1.9\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&1.9x-0.4y-0.8\color{red}+\color{black}0.8x\color{red}+\color{black}0.4y\color{red}+\color{black}1.9\\[5pt]&=&1.9x+0.8x-0.4y+0.4y-0.8+1.9\\[5pt]&=&2.7x+1.1\end{eqnarray}\;\;$

答$2.7x+1.1$

$\begin{eqnarray}(2)\quad\;\;\Bigl(\,-\dfrac{\;a^{2}\;}{\;4\;}+\dfrac{\;a\;}{\;3\;}-\dfrac{\;1\;}{\;2\;}\,\Bigr)-\Bigl(\,\dfrac{\;a^{2}\;}{\;2\;}+\dfrac{a}{\;3\;}+\dfrac{\;3\;}{\;4\;}\,\Bigr)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-\dfrac{\;a^{2}\;}{\;4\;}+\dfrac{\;a\;}{\;3\;}-\dfrac{\;1\;}{\;2\;}\color{red}-\color{black}\dfrac{\;a^{2}\;}{\;2\;}\color{red}-\color{black}\dfrac{a}{\;3\;}\color{red}-\color{black}\dfrac{\;3\;}{\;4\;}\\[6pt]&=&-\dfrac{\;a^{2}\;}{\;4\;}-\dfrac{\;a^{2}\;}{\;2\;}+\dfrac{\;a\;}{\;3\;}-\dfrac{a}{\;3\;}-\dfrac{\;1\;}{\;2\;}-\dfrac{\;3\;}{\;4\;}\\[6pt]&=&-\dfrac{\;1\;}{\;4\;}a^{2}-\dfrac{\;2\;}{\;4\;}a^{2}-\dfrac{\;2\;}{\;4\;}-\dfrac{\;3\;}{\;4\;}\\[6pt]&=&-\dfrac{\;3\;}{\;4\;}a^{2}-\dfrac{\;5\;}{\;4\;}\end{eqnarray}\;\;$

答$-\dfrac{\;3\;}{\;4\;}a^{2}-\dfrac{\;5\;}{\;4\;}$

$\begin{eqnarray}(3)\quad\;\;(\,0.16a^{2}+0.1ab-1.7b^{2}\,)-(\,-0.04a^{2}+0.02ab-0.3b^{2}\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&0.16a^{2}+0.1ab-1.7b^{2}\color{red}+\color{black}0.04a^{2}\color{red}-\color{black}0.02ab\color{red}+\color{black}0.3b^{2}\\[5pt]&=&0.16a^{2}+0.04a^{2}+0.1ab-0.02ab-1.7b^{2}+0.3b^{2}\\[5pt]&=&0.2a^{2}+0.08ab-1.4b^{2}\end{eqnarray}\;\;$

答$0.2a^{2}+0.08ab-1.4b^{2}$

$\begin{eqnarray}(4)\quad\;\;\Bigl(\,-x^{2}+\dfrac{\;xy\;}{\;7\;}-0.2y^{2}\,\Bigr)-\Bigl(\,-\dfrac{3}{\;4\;}x^{2}-2xy-\dfrac{\;y^{2}\;}{10}\,\Bigr)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-x^{2}+\dfrac{\;xy\;}{\;7\;}-0.2y^{2}\color{red}+\color{black}\dfrac{3}{\;4\;}x^{2}\color{red}+\color{black}2xy\color{red}+\color{black}\dfrac{\;y^{2}\;}{10}\\[6pt]&=&-x^{2}+\dfrac{3}{\;4\;}x^{2}+\dfrac{\;xy\;}{\;7\;}+2xy-0.2y^{2}+\dfrac{\;y^{2}\;}{10}\\[6pt]&=&-\dfrac{4}{\;4\;}x^{2}+\dfrac{3}{\;4\;}x^{2}+\dfrac{\;1\;}{\;7\;}xy+\dfrac{\;14\;}{\;7\;}xy-\dfrac{2}{\;10\;}y^{2}+\dfrac{\;1\;}{10}y^{2}\\[6pt]&=&-\dfrac{1}{\;4\;}x^{2}+\dfrac{\;15\;}{\;7\;}xy-\dfrac{1}{\;10\;}y^{2}\end{eqnarray}\;\;$

答$-\dfrac{1}{\;4\;}x^{2}+\dfrac{\;15\;}{\;7\;}xy-\dfrac{1}{\;10\;}y^{2}$

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

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

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$-\dfrac{1}{\,3\,}abc$

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

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

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$-8a^{2}b^{3}c^{3}$

$\begin{eqnarray}(1)\quad\;\;xy \div y\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&\dfrac{\,x \times \color{red}\cancelto{1}{\color{black}y}\,}{\,\color{red}\cancelto{1}{\color{black}y}\,}\\[6pt]&=&x\end{eqnarray}\;\;$

答$x$

$\begin{eqnarray}(2)\quad\;\;2ab \div (\,-ab\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-\dfrac{\,2 \times \color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b}\,}{\,\color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b}\,}\\[6pt]&=&-2\end{eqnarray}\;\;$

答$-\,2$

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

$\begin{eqnarray}\quad\;\;&=&-\dfrac{\,\color{silver}\cancelto{2}{\color{black}4} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times y\,}{\,\color{silver}\cancelto{1}{\color{black}2} \color{black}\times \color{red}\cancelto{1}{\color{black}x}\,}\\[6pt]&=&-2y\end{eqnarray}\;\;$

答$-\,2y$

$\begin{eqnarray}(4)\quad\;\;6ab \div (\,-8ab\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-\dfrac{\,\color{silver}\cancelto{3}{\color{black}6} \color{black}\times \color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b}\,}{\,\color{silver}\cancelto{4}{\color{black}8} \color{black}\times \color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b}\,}\\[6pt]&=&-\dfrac{3}{\;4\;}\end{eqnarray}\;\;$

答$-\,\dfrac{3}{\;4\;}$

$\begin{eqnarray}(5)\quad\;\;(\,-6xyz\,) \div (\,-2xz\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&+\dfrac{\,\color{silver}\cancelto{3}{\color{black}6} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times y \times \color{aqua}\cancelto{1}{\color{black}z}\,}{\,\color{silver}\cancelto{1}{\color{black}2} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{aqua}\cancelto{1}{\color{black}z}\,}\\[6pt]&=&3y\end{eqnarray}\;\;$

答$3y$

$\begin{eqnarray}(1)\quad\;\;x^{2}y \div xy\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&\dfrac{\, \color{red}\cancelto{1}{\color{black}x} \color{black}\times x \times \color{aqua}\cancelto{1}{\color{black}y}\,}{\,\color{red}\cancelto{1}{\color{black}x}\color{black}\times \color{aqua}\cancelto{1}{\color{black}y}\,}\\[6pt]&=&x\end{eqnarray}\;\;$

答$x$

$\begin{eqnarray}(2)\quad\;\;(\,-3a^{2}b^{2}\,) \div ab^{2}\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-\dfrac{\,3 \times \color{red}\cancelto{1}{\color{black}a} \color{black}\times a \times \color{aqua}\cancelto{1}{\color{black}b} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b}\,}{\,\color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b}\,}\\[6pt]&=&-3a\end{eqnarray}\;\;$

答$-\,3a$

$\begin{eqnarray}(3)\quad\;\;16x^{3}y^{2} \div (\,-4x^{2}y\,)\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-\dfrac{\,\color{silver}\cancelto{4}{\color{black}16} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times x \times \color{aqua}\cancelto{1}{\color{black}y} \color{black}\times y\,}{\,\color{silver}\cancelto{1}{\color{black}4} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{aqua}\cancelto{1}{\color{black}y}\,}\\[6pt]&=&-4xy\end{eqnarray}\;\;$

答$-\,4xy$

$\begin{eqnarray}(4)\quad\;\;(\,-28a^{2}b^{3}\,) \div 7a^{2}b\end{eqnarray}\;\;$

$\begin{eqnarray}\quad\;\;&=&-\dfrac{\,\color{silver}\cancelto{4}{\color{black}28} \color{black}\times \color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b} \color{black}\times b \color{black}\times b\,}{\,\color{silver}\cancelto{1}{\color{black}7} \color{black}\times \color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{red}\cancelto{1}{\color{black}a} \color{black}\times \color{aqua}\cancelto{1}{\color{black}b}\,}\\[6pt]&=&-4b^{2}\end{eqnarray}\;\;$

答$-\,4b^{2}$

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

$\begin{eqnarray}\quad\;\;&=&+\dfrac{\,5\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times x \times \color{aqua}\cancelto{1}{\color{black}y} \color{black}\times \color{aqua}\cancelto{1}{\color{black}y}\,}{\,3 \times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{red}\cancelto{1}{\color{black}x} \color{black}\times \color{aqua}\cancelto{1}{\color{black}y} \color{black}\times \color{aqua}\cancelto{1}{\color{black}y}\,}\\[6pt]&=&\dfrac{5}{\;3\;}x\end{eqnarray}\;\;$

答$\dfrac{5}{\;3\;}x$