4.318 Найдите х из пропорции: x a) -7,3; -1,4 = -2,8 -8,4 -12,6 б) =; 105 х 1 B) -2,5x 7; 14 = -30 -71 х 7 3 г) = . 2 1 4- 25

Ответ:

a) \[\frac{x}{-1,4} = \frac{-7,3}{-2,8}\]

\[x = \frac{(-1,4) \cdot (-7,3)}{-2,8} = \frac{1,4 \cdot 7,3}{2,8} = \frac{7,3}{2} = 3,65\]

б) \[\frac{-8,4}{105} = \frac{-12,6}{x}\]

\[x = \frac{105 \cdot (-12,6)}{-8,4} = \frac{105 \cdot 12,6}{8,4} = \frac{105 \cdot 126}{84} = \frac{105 \cdot 3}{2} = \frac{315}{2} = 157,5\]

в) \[\frac{-2,5x}{14} = \frac{7}{-30}\]

\[-2,5x = \frac{14 \cdot 7}{-30}\]

\[-2,5x = \frac{14 \cdot 7}{-30}\]

\[x = \frac{14 \cdot 7}{2,5 \cdot 30} = \frac{14 \cdot 7}{2,5 \cdot 30} = \frac{14 \cdot 7 \cdot 10}{25 \cdot 30} = \frac{14 \cdot 7 \cdot 2}{5 \cdot 30} = \frac{14 \cdot 7}{5 \cdot 15} = \frac{98}{75} = 1\frac{23}{75}\]

г) \[-\frac{7\frac{1}{2}}{4\frac{1}{2}} = \frac{x}{\frac{3}{25}}\]

\[\frac{-\frac{15}{2}}{\frac{9}{2}} = \frac{x}{\frac{3}{25}}\]

\[x = \frac{-\frac{15}{2} \cdot \frac{3}{25}}{\frac{9}{2}} = -\frac{15 \cdot 3 \cdot 2}{2 \cdot 25 \cdot 9} = -\frac{3 \cdot 3}{25 \cdot 3} = -\frac{1}{5}\]

Ответ: