数学演習中学校1年生/文字の式/解答

文字式の表し方

$5 x + 3 x = (5 + 3) x = 8 x$
$5 a - 4 a = (5 - 4) a = a$
$7 a + 3 - 5 a - 6 = 7 a - 5 a + 3 - 6 = (7 - 5) a + (3 - 6) = 2 a - 3$
$3 x - 2 - x + 9 = 3 x + x - 2 + 9 = (3 - 1) x + (- 2 + 9) = 2 x + 7$
$(3 a + 2) + (6 a - 5) = 3 a + 2 + 6 a - 5 = 9 a - 3$
$(5 x - 9) + (- 3 x + 9) = 5 x - 9 - 3 x + 9 = 2 x$
$\begin{matrix} (5 a - 3) - (3 a + 2) & = & (5 a - 3) + (- 3 a - 2) \\ = & 5 a - 3 - 3 a - 2 & = & 2 a - 5 \end{matrix}$
$\begin{matrix} (a - 7) - (2 a + 7) & = & (a - 7) + (- 2 a - 7) \\ = & a - 7 - 2 a - 7 & = & - a - 14 \end{matrix}$

$3 x \times 4 = 3 \times x \times 4 = 3 \times 4 \times x = 12 x$
$\frac{2}{5} a \times (- 10) = \frac{2}{5} \times a \times (- 10) = \frac{2}{5} \times (- 10) \times a = - 4 a$
$3 (x + 6) = 3 \times x + 3 \times 6 = 3 x + 18$
$- 4 (2 x - 5) = (- 4) \times 2 x + (- 4) \times (- 5) = - 8 x + 20$
$\frac{5 a - 3}{7} \times 14 = \frac{(5 a - 3) \times 14}{7} = 2 (5 a - 3) = 10 a - 6$
$12 x \div 6 = 12 x \times \frac{1}{6} = 2 x$
$9 a \div \frac{3}{4} = 9 a \times \frac{4}{3} = 12 a$
$(18 a - 15) \div 3 = (18 a - 15) \times \frac{1}{3} = 6 a - 5$
$(24 a - 8) \div (- 8) = (24 a - 8) \times (- \frac{1}{8}) = - 3 a + 1$
$6 (a + 2) + 5 (2 a - 3) = 6 a + 12 + 10 a - 15 = 16 a - 3$
$2 (x + 3) - 3 (2 x - 1) = 2 x + 6 - 6 x + 3 = - 4 x + 9$