5.101 Найдите х из пропорции: a) x-4 8 5 6) 3x + 2 = 7 4 2,5 27,5

a)

\[\frac{x-4}{8} = \frac{7}{4}\]

\[4(x - 4) = 8 \cdot 7\]

\[4x - 16 = 56\]

\[4x = 56 + 16\]

\[4x = 72\]

\[x = \frac{72}{4}\]

\[x = 18\]

Ответ: x = 18

б)

\[\frac{5}{3x+2} = \frac{2.5}{27.5}\]

\[2.5(3x + 2) = 5 \cdot 27.5\]

\[7.5x + 5 = 137.5\]

\[7.5x = 137.5 - 5\]

\[7.5x = 132.5\]

\[x = \frac{132.5}{7.5}\]

\[x = \frac{1325}{75}\]

\[x = \frac{53}{3}\]

\[x = 17\frac{2}{3}\]

Ответ: x = 17\frac{2}{3}