Đáp án:
Bài 1 :
$a. \frac{x}{12} = \frac{y}{5}$
$b. \frac{x}{y} = \frac{3}{5} ⇒ \frac{x}{3} = \frac{y}{5}$
$c. \frac{x}{2} = \frac{y}{-9}$
$d. \frac{x}{1} = \frac{y}{3}$
Bài 2 :
$a. \frac{x}{5} = \frac{y}{12}$
$b. \frac{x}{1} = \frac{y}{-6}$
$c. \frac{x}{1} = \frac{y}{-2}$
Bài 3 :
$a. \frac{a}{20} = \frac{b}{15} = \frac{c}{12}$
$b. \frac{a}{63} = \frac{b}{45} = \frac{c}{35}$
$c. \frac{a}{-6} = \frac{b}{3} = \frac{c}{-2}$
Giải thích các bước giải:
Bài 1 :
$a. \frac{x}{y} = \frac{12}{5}$
⇒ $\frac{x}{12} = \frac{y}{5}$
$b. \frac{x}{y} = 0,6$
⇒ $\frac{x}{y} = \frac{3}{5}$
⇒ $\frac{x}{3} = \frac{y}{5}$
$c. \frac{y}{x} = \frac{-9}{2}$
⇒ $\frac{x}{2} = \frac{y}{-9}$
$d. \frac{y}{x} = 3$
⇒ $\frac{x}{1} = \frac{y}{3}$
Bài 2 :
$a. 12x = 5y$
⇒ $\frac{x}{5} = \frac{y}{12}$
$b. -18x = 3y ⇔ -6x = y$
⇒ $\frac{x}{1} = \frac{y}{-6}$
$c. -2x = y$
⇒ $\frac{x}{1} = \frac{y}{-2}$
Bài 3 :
$a. 6a = 8b = 10c ⇔ 3a = 4b = 5c$
⇒ $\frac{3a}{3×4×5} = \frac{4b}{3×4×5} = \frac{5c}{3×4×5}$
⇒ $\frac{a}{20} = \frac{b}{15} = \frac{c}{12}$
$b. 5a = 7b = 9c$
⇒ $\frac{5a}{5×7×9} = \frac{7b}{5×7×9} = \frac{9c}{5×7×9}$
⇒ $\frac{a}{63} = \frac{b}{45} = \frac{c}{35}$
$c. -2a = 4b = -6c ⇒ - a = 2b = -3c$
⇒ $\frac{-a}{-1×2×(-3)} = \frac{2b}{-1×2×(-3)} = \frac{-3c}{-1×2×(-3)}$
⇒ $\frac{a}{-6} = \frac{b}{3} = \frac{c}{-2}$
