Tìm giá trị của x , biết: (a) x/15 = − 70/105 . (b) 5/2 + − 1/2 x = 1/3 .

a) \(\frac{x}{{15}} = \frac{{ - 70}}{{105}}\)

\(\frac{x}{{15}} = \frac{{ - 2}}{3}\)

\(x = \frac{{\left( { - 2} \right) \cdot 15}}{3}\)

\(x = - 10.\)

Vậy \(x = - 10.\)

b) \(\frac{5}{2} + \frac{{ - 1}}{2}x = \frac{1}{3}\)

\(\frac{{ - 1}}{2}x = \frac{1}{3} - \frac{5}{2}\)

\(\frac{{ - 1}}{2}x = \frac{{ - 13}}{6}\)

\(x = \frac{{ - 13}}{6}:\frac{{ - 1}}{2}\)

\(x = \frac{{13}}{3}.\)

Vậy \(x = \frac{{13}}{3}.\)