---

(3) $\;\;\;\begin{eqnarray}-24a\Bigl(-\frac{5}{\;8\;}a+\frac{7}{\;12\;}b\Bigr)\end{eqnarray}\;\;$

$\;\;\;\begin{eqnarray}&=& -24a\times\Bigl(-\frac{5}{\;8\;}a\Bigr)-24a\times\frac{7}{\;12\;}b \\[5pt]&=&15a^{2}-14ab\end{eqnarray}\;\;$

答$\;\;\begin{eqnarray} 15a^{2}-14ab \end{eqnarray}$

---

(4) $\;\;\;\begin{eqnarray}(4a-b)\times (-5a)\end{eqnarray}\;\;$

$\;\;\;\begin{eqnarray}&=& 4a\times (-5a)-b\times (-5a)\\[5pt]&=&-20a^{2}+5ab\end{eqnarray}\;\;$

答$\;\;\begin{eqnarray} -20a^{2}+5ab \end{eqnarray}$

---

(5) $\;\;\;\begin{eqnarray} (-10x-15y)\times\frac{2}{\;5\;}x\end{eqnarray}\;\;$

$\;\;\;\begin{eqnarray}&=&-10x\times \frac{2}{\;5\;}x -15y\times \frac{2}{\;5\;}x \\[5pt]&=&-4x^{2}-6xy\end{eqnarray}\;\;$

答$\;\;\begin{eqnarray} -4x^{2}-6xy \end{eqnarray}$

(1) $\;\;\;\begin{eqnarray}3a(2a-4b+5c)\end{eqnarray}\;\;$

$\;\;\begin{eqnarray}&=&3a \times 2a+3a \times (-4b)+3a \times 5c\\[5pt]&=&6a^{2}-12ab+15ac\end{eqnarray}\;\;$

答$6a^{2}-12ab+15ac$

---

(2) $\;\;\;\begin{eqnarray} -7x(-x+2y-1) \end{eqnarray}\;\;$

$\;\;\begin{eqnarray}&=&-7x \times (-x)-7x\times 2y -7x\times (-1)\\[5pt]&=&7x^{2}-14xy+7x\end{eqnarray}\;\;$

答$7x^{2}-14xy+7x$

---

(3) $\,\;\;\;\begin{eqnarray}-\frac{2}{\;3\;}a(6a-12b-21c)\end{eqnarray}\;\;$

$\;\;\begin{eqnarray} &=& -\frac{2}{\;3\;}a \times 6a -\frac{2}{\;3\;}a \times (-12b) -\frac{2}{\;3\;}a \times (-21c) \\[5pt]&=&-4a^{2}+8ab+14ac\end{eqnarray}\;\;$

答$-4a^{2}+8ab+14ac$

---

(4) $\;\;\begin{eqnarray}(9x-4xy+3y)\times (-5x)\end{eqnarray}\;\;$

$\;\;\begin{eqnarray} &=& 9x\times (-5x)-4xy\times (-5x)+3y\times (-5x)\\[5pt]&=&-45x^{2}+20x^{2}y-15xy\end{eqnarray}\;\;$

答$-45x^{2}+20x^{2}y-15xy$

---

(5) $\;\;\;\begin{eqnarray} (-8a-20ab+16b)\times \Bigl(-\frac{b}{\;4\;}\Bigr)\end{eqnarray}\;\;$

$\;\;\begin{eqnarray} &=& -8a\times \Bigl(-\frac{b}{\;4\;}\Bigr) -20ab\times \Bigl(-\frac{b}{\;4\;}\Bigr) +16b\times \Bigl(-\frac{b}{\;4\;}\Bigr) \\[5pt]&=& 2ab+5ab^{2}-4b^{2}\end{eqnarray}\;\;$

答$2ab+5ab^{2}-4b^{2}$

(1) $\;\;\begin{eqnarray}(20ab-12b)\div 4b\end{eqnarray}\;\;$

割る数を逆数にして乗法で展開します

$\qquad\begin{eqnarray} (20ab-12b)\div 4b &=& (20ab-12b)\times \frac{1}{\;4b\;}\\[5pt]&=& 20ab\times\frac{1}{\;4b\;}-12b\times \frac{1}{\;4b\;}\\[5pt] &=& 5a-3\end{eqnarray}\;\;$

答$5a-3$

---

(2) $\;\;\begin{eqnarray} (-2x^{2}+4xy)\div (-2x) \end{eqnarray}\;\;$

割る数を逆数にして乗法で展開します

$\qquad\begin{eqnarray} (-2x^{2}+4xy)\div (-2x)\end{eqnarray}\;\;$

$\quad\begin{eqnarray} &=&(-2x^{2}+4xy)\times \Bigl(-\frac{1}{\;2x\;}\Bigr)\\[5pt] &=& -2x^{2}\times \Bigl(-\frac{1}{\;2x\;}\Bigr) +4xy \times \Bigl(-\frac{1}{\;2x\;}\Bigr) \\[5pt] &=& x-2y \end{eqnarray}\;\;$

答$x-2y$

---

(3) $\;\;\begin{eqnarray}(15a^{2}b-30ab-45ab^{2})\div (-5ab)\end{eqnarray}\;\;$

割る数を逆数にして乗法で展開します

$\;\qquad\begin{eqnarray} (15a^{2}b-30ab-45ab^{2})\div (-5ab) \end{eqnarray}\;\;$

$\quad\begin{eqnarray} &=& (15a^{2}b-30ab-45ab^{2})\times \Bigl( -\frac{1}{\;5ab\;}\Bigr) \\[5pt] &=& 15a^{2}b\times \Bigl( -\frac{1}{\;5ab\;}\Bigr) -30ab\times \Bigl( -\frac{1}{\;5ab\;}\Bigr) -45ab^{2}\times \Bigl( -\frac{1}{\;5ab\;}\Bigr) \\[5pt]&=& -3a+6+9b \end{eqnarray}\;\;$

答$-3a+6+9b$

---

(4) $\;\;\begin{eqnarray}(14x^{2}-21xy)\div \frac{7}{\;3\;}x \end{eqnarray}\;\;$

割る数を逆数にして乗法で展開します

$\qquad\begin{eqnarray} (14x^{2}-21xy) \div \dfrac{7}{\;3\;}x\end{eqnarray}\;\;$

$\quad\begin{eqnarray} &=& (14x^{2}-21xy)\times \frac{3}{\;7x\;}\\[5pt]&=&14x^{2}\times \frac{3}{\;7x\;} -21xy\times \frac{3}{\;7x\;} \\[5pt] &=& 6x-9y\end{eqnarray}\;\;$

答$6x-9y$

---

(5) $\;\;\begin{eqnarray} (6x^{2}y-18xy+30xy^{2})\div \Bigl(-\frac{3}{\;2\;}xy\Bigr) \end{eqnarray}\;\;$

割る数を逆数にして乗法で展開します

$\;\qquad\begin{eqnarray} (6x^{2}y-18xy+30xy^{2})\div \Bigl(-\frac{3}{\;2\;}xy\Bigr) \end{eqnarray}\;\;$

$\quad\begin{eqnarray} &=& (6x^{2}y-18xy+30xy^{2})\times \Bigl(-\frac{2}{\;3xy\;}\Bigr) \\[5pt]&=& 6x^{2}y \times \Bigl(-\frac{2}{\;3xy\;}\Bigr) -18xy \times \Bigl(-\frac{2}{\;3xy\;}\Bigr) +30xy^{2} \times \Bigl(-\frac{2}{\;3xy\;}\Bigr) \\[5pt] &=& -4x+12-20y \end{eqnarray}\;\;$

答$-4x+12-20y$

(1) $\;\;\begin{eqnarray}(\,x+a\,)(\,y+b\,)\end{eqnarray}\;\;$

分配法則を利用して展開します

答$xy+bx+ay+ab$

---

(2) $\;\;\begin{eqnarray}(\,x-y\,)(\,a-b\,)\end{eqnarray}\;\;$

分配法則を利用して展開します

答$ax-bx-ay+by$

---

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

分配法則を利用して展開します

答$-ac+2a+bc-2b$

---

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

分配法則を利用して展開します

答$-xy-5x-3y-15$

---

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

分配法則を利用して展開します

答$ab+7a+2b+14$

(1) $\;\;\begin{eqnarray}(a+2)(a+b+3)\end{eqnarray}\;\;$

$\qquad$ 解法１

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

$\qquad\begin{eqnarray}&=&a(a+b+3)+2(a+b+3)\\[3pt]&=&a^{2}+ab+3a+2a+2b+6\\[3pt]&=&a^{2}+ab+5a+2b+6\end{eqnarray}\;\;$

$\qquad$ 解法２

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

$\qquad\begin{eqnarray} &=&a\times a+a\times b+a\times 3+2\times a+2\times b+2\times 3\\[3pt] &=&a^{2}+ab+3a+2a+2b+6\\[3pt]&=&a^{2}+ab+5a+2b+6\end{eqnarray}\;\;$

答$a^{2}+ab+5a+2b+6$

---

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

$\qquad$ 解法１

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

$\qquad\begin{eqnarray}&=&x(2x+3y-5)-y(2x+3y-5)\\[3pt]&=&2x^{2}+3xy-5x-2xy-3y^{2}+5y\\[3pt]&=&2x^{2}+xy-5x-3y^{2}+5y\end{eqnarray}\;\;$

$\qquad$ 解法２

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

$\qquad\begin{eqnarray}&=&x \hspace{-0.2em} \times \hspace{-0.2em} 2x+x \hspace{-0.2em} \times \hspace{-0.2em} 3y+x \hspace{-0.2em} \times \hspace{-0.2em} (-5)-y \hspace{-0.2em} \times \hspace{-0.2em} 2x-y \hspace{-0.2em} \times \hspace{-0.2em} 3y-y \hspace{-0.2em} \times \hspace{-0.2em} (-5)\\[3pt]&=&2x^{2}+3xy-5x-2xy-3y^{2}+5y\\[3pt]&=&2x^{2}+xy-5x-3y^{2}+5y\end{eqnarray}\;\;$

答$2x^{2}+xy-5x-3y^{2}+5y$

---

(3) $\;\;\begin{eqnarray}(3a-b-8)(2a-3b)\end{eqnarray}\;\;$

$\qquad$ 解法１

$\quad\qquad\begin{eqnarray}(3a-b-8)(2a-3b)\end{eqnarray}\;\;$

$\qquad\begin{eqnarray}&=&3a(2a-3b)-b(2a-3b)-8(2a-3b)\\[3pt]&=&6a^{2}-9ab-2ab+3b^{2}-16a+24b\\[3pt]&=&6a^{2}-11ab+3b^{2}-16a+24b\end{eqnarray}\;\;$

$\qquad$ 解法２

$\quad\qquad\begin{eqnarray}(3a-b-8)(2a-3b)\end{eqnarray}\;\;$

$\qquad\begin{eqnarray}&=&3a\hspace{-0.3em}\times \hspace{-0.3em} 2a+3a \hspace{-0.3em} \times \hspace{-0.3em} (-3b)-b \hspace{-0.3em} \times \hspace{-0.3em} 2a-b \hspace{-0.3em} \times \hspace{-0.3em} (-3b)-8 \hspace{-0.3em} \times \hspace{-0.3em} 2a-8 \hspace{-0.3em} \times \hspace{-0.3em} (-3b) \\[3pt]&=&6a^{2}-9ab-2ab+3b^{2}-16a+24b\\[3pt]&=&6a^{2}-11ab+3b^{2}-16a+24b+6\end{eqnarray}\;\;$

答$6a^{2}-11ab+3b^{2}-16a+24b$

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

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

答$x^{2}+5x+6$

---

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

$\;\;\begin{eqnarray}&=&x^{2}+\{\,3+(\,-4\,)\}x+\{\,3\times(-4)\}\\[6pt]&=&x^{2}-x-12\end{eqnarray}\;\;$

答$x^{2}-x-12$

---

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

$\;\;\begin{eqnarray}&=&x^{2}+\{\,(-5)+8\,\}x+\{(\,-5\,) \times 8\,\}\\[6pt]&=&x^{2}+3x-40\end{eqnarray}\;\;$

答$x^{2}+3x-40$

---

(4) $\quad\;\,\begin{eqnarray}(\,x-4\,)(\,x-7\,)\end{eqnarray}\;\;$

$\;\;\begin{eqnarray}&=&x^{2}+\{\,(-4)+(-7)\,\}x+\{(\,-4\,) \times (-7)\}\\[6pt]&=&x^{2}-11x+28\end{eqnarray}\;\;$

答$x^{2}-11x+28$

---

(5) $\quad\;\,\begin{eqnarray}(\,x+0.6\,)(\,x-0.9\,)\end{eqnarray}\;\;$

$\;\;\begin{eqnarray}&=&x^{2}+\{\,0.6+(-0.9)\,\}x+\{\,0.6\times (\,-0.9\,)\}\\[6pt]&=&x^{2}-0.3x-0.54\end{eqnarray}\;\;$

答$x^{2}-0.3x-0.54$

---

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

$\;\;\begin{eqnarray}&=&x^{2}+\Bigl\{\,\frac{1}{\;2\;}+\Bigl(\,-\frac{2}{\;3\;}\,\Bigr)\Bigr\}x+\Bigl\{\,\frac{1}{\;2\;}\times \Bigl(-\frac{2}{\;3\;}\Bigr)\Bigr\}\\[6pt]&=&x^{2}-\frac{1}{\;6\;}x-\frac{1}{\;3\;}\end{eqnarray}\;\;$

答$x^{2}-\dfrac{1}{\;6\;}x-\dfrac{1}{\;3\;}$

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

$\;\;\begin{eqnarray}&=&(\,2x\,)^{2}+(\,3+5\,) \times 2x+(\,3\times 5\,)\\[6pt]&=&4x^{2}+16x+15\end{eqnarray}\;\;$

答$4x^{2}+16x+15$

---

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

$\;\;\begin{eqnarray}&=&(\,3x\,)^{2}+\{\,(\,-5\,)+(\,-4\,)\} \times 3x+ \{(\,-5\,) \times (\,-4\,)\}\\[6pt]&=&9x^{2}-27x+20\end{eqnarray}\;\;$

答$9x^{2}-27x+20$

---

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

$\;\;\begin{eqnarray}&=&(\,5x\,)^{2}+\{\,5+(-1)\} \times 5x+\{\,5 \times (\,-1\,)\}\\[6pt]&=&25x^{2}+20x-5\end{eqnarray}\;\;$

答$25x^{2}+20x-5$

---

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

$\;\;\begin{eqnarray}&=&(\,-x\,)^{2}+\{\,2+(\,-6\,)\} \times (\,-x\,)+\{\,2 \times (\,-6\,)\}\\[6pt]&=&x^{2}+4x-12\end{eqnarray}\;\;$

《 別解 》

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

$\;\;\begin{eqnarray}&=&\{-(\,x-2\,)\}\{-(\,x+6\,)\}\\[6pt]&=&(\,x-2\,)(\,x+6\,)\\[6pt]&=&x^{2}+\{(\,-2\,)+6\,\} \times x+\{(\,-2\,) \times 6\}\\[6pt]&=&x^{2}+4x-12\end{eqnarray}\;\;$

答$x^{2}+4x-12$

---

(5) $\quad\;\,\begin{eqnarray}(\,8-4x\,)(\,7-4x\,)\end{eqnarray}\;\;$

$\;\;\begin{eqnarray}&=&(\,-4x+8\,)(\,-4x+7\,)\\[6pt]&=&(\,-4x\,)^{2}+(\,8+7\,) \times (\,-4x\,)+(\,8 \times 7\,)\\[6pt]&=&16x^{2}-60x+56\end{eqnarray}\;\;$

《 別解 》

$\quad\;\;\;\begin{eqnarray}(\,8-4x\,)(\,7-4x\,)\end{eqnarray}\;\;$

$\;\;\begin{eqnarray}&=&(\,-4x+8\,)(\,-4x+7\,)\\[6pt]&=&\{-(\,4x-8\,)\}\{-(\,4x-7\,)\}\\[6pt]&=&(\,4x-8\,)(\,4x-7\,)\\[6pt]&=&(\,4x\,)^{2}+\{(\,-8\,)+(\,-7\,)\} \times 4x+\{(\,-8\,) \times (\,-7\,)\}\\[6pt]&=&16x^{2}-60x+56\end{eqnarray}\;\;$

答$16x^{2}-60x+56$

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

$\;\;\begin{eqnarray}&=&(\,2x\,)^{2}+(\,y+5y\,) \times 2x+(\,y\times 5y\,)\\[6pt]&=&4x^{2}+12xy+5y^{2}\end{eqnarray}\;\;$

答$4x^{2}+12xy+5y^{2}$

---

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

$\;\;\begin{eqnarray}&=&(\,4x\,)^{2}+\{\,(\,-3y\,)+(\,-7y\,)\} \times 4x+ \{(\,-3y\,) \times (\,-7y\,)\}\\[6pt]&=&16x^{2}-40xy+21y^{2}\end{eqnarray}\;\;$

答$16x^{2}-40xy+21y^{2}$

---

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

$\;\;\begin{eqnarray}&=&(\,6x\,)^{2}+\{\,5y+(-4y)\} \times 6x+\{\,5y \times (\,-4y\,)\}\\[6pt]&=&36x^{2}+6xy-20y^{2}\end{eqnarray}\;\;$

答$36x^{2}+6xy-20y^{2}$

---

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

$\;\;\begin{eqnarray}&=&(\,-3x\,)^{2}+\{(\,-7y\,)+8y\,\} \times (\,-3x\,)+\{(\,-7y\,) \times 8y\,\}\\[6pt]&=&9x^{2}-3xy-56y^{2}\end{eqnarray}\;\;$

《 別解 》

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

$\;\;\begin{eqnarray}&=&\{-(\,3x+7y\,)\}\{-(\,3x-8y\,)\}\\[6pt]&=&(\,3x+7y\,)(\,3x-8y\,)\\[6pt]&=&(\,3x\,)^{2}+\{\,7y+(\,-8y\,)\} \times 3x +\{\,7y \times (\,-8y\,)\}\\[6pt]&=&9x^{2}-3xy-56y^{2}\end{eqnarray}\;\;$

答$9x^{2}-3xy-56y^{2}$

---

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

$\;\;\begin{eqnarray}&=&(\,-3y+2x\,)(\,-3y+5x\,)\\[6pt]&=&(\,-3y\,)^{2}+(\,2x+5x\,) \times (\,-3y\,)+(\,2x \times 5x\,)\\[6pt]&=&9y^{2}-21xy+10x^{2}\end{eqnarray}\;\;$

《 別解 》

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

$\;\;\begin{eqnarray}&=&(\,-3y+2x\,)(\,-3y+5x\,)\\[6pt]&=&\{-(\,3y-2x\,)\}\{-(\,3y-5x\,)\}\\[6pt]&=&(\,3y-2x\,)(\,3y-5x\,)\\[6pt]&=&(\,3y\,)^{2}+\{(\,-2x\,)+(\,-5x\,)\} \times 4x+\{(\,-2x\,) \times (\,-5x\,)\}\\[6pt]&=&9y^{2}-21xy+10x^{2}\end{eqnarray}\;\;$

答$9y^{2}-21xy+10x^{2}$

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

$\;\;\begin{eqnarray}&=&x^{2}+2\times 2\times x+2^{2}\\[6pt]&=&x^{2}+4x+4\end{eqnarray}\;\;$

答$x^{2}+4x+4$

---

(2) $\quad\;\,\begin{eqnarray}(\,x+10\,)^{2}\end{eqnarray}$

$\;\;\begin{eqnarray}&=&x^{2}+2\times 10\times x+10^{2}\\[6pt]&=&x^{2}+20x+100\end{eqnarray}\;\;$

答$x^{2}+20x+100$

---

(3) $\quad\;\,\begin{eqnarray}(\,x+0.6\,)^{2}\end{eqnarray}$

$\;\;\begin{eqnarray}&=&x^{2}+2\times 0.6\times x+0.6^{2}\\[6pt]&=&x^{2}+1.2x+0.36\end{eqnarray}\;\;$

答$x^{2}+1.2x+0.36$

---

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

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

答$x^{2}-2x+1$

---

(5) $\quad\;\,\begin{eqnarray}\Bigl(\,x-\frac{2}{3}\,\Bigr)^{2}\end{eqnarray}\;\;$

$\;\;\begin{eqnarray}&=&x^{2}-2\times \frac{2}{\;3\;}\times x +\Bigl(\,-\frac{2}{\;3\;}\,\Bigr)^{2}\\[6pt]&=&x^{2}-\frac{4}{\;3\;}x+\frac{4}{\;9\;}\end{eqnarray}\;\;$

答$x^{2}-\dfrac{4}{\;3\;}x+\dfrac{4}{\;9\;}$

---

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

$\;\;\begin{eqnarray}&=&4^{2}-2\times x\times 4+x^{2}\\[6pt]&=&16-8x+x^{2}\\[6pt]&=&x^{2}-8x+16\end{eqnarray}\;\;$

答$x^{2}-8x+16$

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

$\;\;\begin{eqnarray}&=&(\,2x\,)^{2}+2\times 2\times 2x+2^{2}\\[6pt]&=&4x^{2}+8x+4\end{eqnarray}\;\;$

答$4x^{2}+8x+4$

---

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

$\;\;\begin{eqnarray}&=&(\,5x\,)^{2}+2\times 4 \times 5x + 4^{2}\\[6pt]&=&25x^{2}+40x+16\end{eqnarray}\;\;$

答$25x^{2}+40x+16$

---

(3) $\quad\;\,\begin{eqnarray}(\,0.2x+5\,)^{2}\end{eqnarray}$

$\;\;\begin{eqnarray}&=&(\,0.2x\,)^{2}+2\times 5 \times 0.2x + 5^{2}\\[6pt]&=&0.04x^{2}+2x+25\end{eqnarray}\;\;$

答$0.04x^{2}+2x+25$

---

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

$\;\;\begin{eqnarray}&=&(\,4x\,)^{2}-2\times 1 \times 4x+1^{2}\\[6pt]&=&16x^{2}-8x+1\end{eqnarray}\;\;$

答$16x^{2}-8x+1$

---

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

$\;\;\begin{eqnarray}&=&\Bigl(\dfrac{\;1\;}{\;2\;}x\Bigr)^{2}-2\times \dfrac{\;1\;}{\;3\;}\times \dfrac{\;1\;}{\;2\;}x +\Bigl(\,\dfrac{1}{\;3\;}\,\Bigr)^{2}\\[6pt]&=&\dfrac{\;1\;}{\;4\;}x^{2}- \dfrac{\;1\;}{\;3\;}x +\dfrac{1}{\;9\;}\end{eqnarray}\;\;$

答$\dfrac{\;1\;}{\;4\;}x^{2}- \dfrac{\;1\;}{\;3\;}x +\dfrac{1}{\;9\;}$

---

(6) $\quad\;\,\begin{eqnarray}(\,10-0.1x\,)^{2}\end{eqnarray}\;\;$

$\;\;\begin{eqnarray}&=&10^{2}-2\times 0.1x \times 10+(\,0.1x\,)^{2}\\[6pt]&=&100-2x+0.01x^{2}\\[6pt]&=&0.01x^{2}-2x+100\end{eqnarray}\;\;$

答$0.01x^{2}-2x+100$