3. Решите уравнения, используя основное свойство пропорции: 1. x/3 = 15/5 2. 9/x = 18/6 3. x/8 = 12/4 4. 7/x = 21/3

Решение:

1. \[\frac{x}{3} = \frac{15}{5}\] \[5x = 3 \cdot 15\] \[5x = 45\] \[x = \frac{45}{5}\] \[x = 9\]
2. \[\frac{9}{x} = \frac{18}{6}\] \[9 \cdot 6 = 18x\] \[54 = 18x\] \[x = \frac{54}{18}\] \[x = 3\]
3. \[\frac{x}{8} = \frac{12}{4}\] \[4x = 8 \cdot 12\] \[4x = 96\] \[x = \frac{96}{4}\] \[x = 24\]
4. \[\frac{7}{x} = \frac{21}{3}\] \[7 \cdot 3 = 21x\] \[21 = 21x\] \[x = \frac{21}{21}\] \[x = 1\]

Ответ: 1. x=9, 2. x=3, 3. x=24, 4. x=1