4.318 Найдите х из пропорции: a) \(\frac{x}{-1,4} = \frac{-7,3}{-2,8}\); б) \(\frac{-8,4}{105} = \frac{-12,6}{x}\); в) \(\frac{-2,5x}{14} = \frac{1}{-30}\); г) \(\frac{-7\frac{1}{2}}{2} = \frac{4\frac{1}{4}}{x}\)

Решение:

а) \(\frac{x}{-1,4} = \frac{-7,3}{-2,8}\) \(x = \frac{(-1,4) \cdot (-7,3)}{-2,8}\) \(x = \frac{10,22}{-2,8}\) \(x = -3,65\) б) \(\frac{-8,4}{105} = \frac{-12,6}{x}\) \(x = \frac{105 \cdot (-12,6)}{-8,4}\) \(x = \frac{-1323}{-8,4}\) \(x = 157,5\) в) \(\frac{-2,5x}{14} = \frac{1}{-30}\) \(-2,5x = \frac{14 \cdot 1}{-30}\) \(-2,5x = \frac{14}{-30}\) \(x = \frac{14}{-30 \cdot (-2,5)}\) \(x = \frac{14}{75}\) \(x = 0,1866... \approx 0,19\) г) \(\frac{-7\frac{1}{2}}{2} = \frac{4\frac{1}{4}}{x}\) \(\frac{-\frac{15}{2}}{2} = \frac{\frac{17}{4}}{x}\) \(x = \frac{2 \cdot \frac{17}{4}}{-\frac{15}{2}}\) \(x = \frac{\frac{17}{2}}{-\frac{15}{2}}\) \(x = \frac{17}{2} \cdot (-\frac{2}{15})\) \(x = -\frac{17}{15}\) \(x = -1\frac{2}{15}\)

Ответ: а) -3,65; б) 157,5; в) \(\frac{14}{75}\); г) -1\frac{2}{15}