\[t,\ ч\] | \[V,\ \frac{км}{ч}\] | \[S,\ км\] | |
---|---|---|---|
\[І\ дорога\] | \[\frac{48}{x}\] | \[x\] | \[48\] |
\[ІІ\ дорога\] | \[\frac{40}{x + 4}\ на\ 1\ ч < \nwarrow\] | \[x + 4\] | \[40\] |
\[\mathbf{Составим\ уравнение:}\]
\[\frac{48}{x} - \frac{40}{x + 4} = 1\]
\[\frac{48 \cdot (x + 4) - 40x}{x(x + 4)} = 1\]
\[48x + 192 - 40x = x^{2} + 4x\]
\[8x + 192 = x^{2} + 4x\]
\[x^{2} + 4x - 8x - 192 = 0\]
\[x^{2} - 4x - 192 = 0\]
\[D = b^{2} - 4ac = 16 - 4 \cdot 1 \cdot ( - 192) =\]
\[= 16 + 768 = 784\]
\[x_{1} = \frac{4 + 28}{2} = \frac{32}{2} = 16\]
\[x_{2} = \frac{4 - 28}{2} = - \frac{24}{2} = - 12 < 0 \Longrightarrow\]
\[\Longrightarrow не\ подходит.\]
\[Ответ:по\ первой\ дороге\ велосипедист\ \]
\[ехал\ со\ скоростью\ 16\ \frac{км}{ч}.\]
\[\ \frac{5x + 14}{x^{2} - 4} = \frac{x^{2}}{x^{2} - 4}\]
\[ОДЗ:\ \ x^{2} - 4 \neq 0\]
\[\text{\ \ \ \ \ \ \ \ \ \ \ x} \neq \pm 2\]
\[5x + 14 = x^{2}\]
\[x^{2} - 5x - 14 = 0\]
\[x_{1} + x_{2} = 5\]
\[x_{1} \cdot x_{2} = - 14 \Longrightarrow x_{1} = 7\ \ \ и\ \ \ x_{2} = - 2\ \]
\[(не\ подходит).\]
\[Ответ:\ \ x = 7.\]
\[\ \]