Tìm giá trị của x , biết (a) x + 1/3 = − 1/5 . (b) ( 2/7 − x ) + 1/5 = 3/5 .

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

\(\begin{array}{l}x = \frac{{ - 1}}{5} - \frac{1}{3}\\x = \frac{{ - 8}}{{15}}\end{array}\)

b) \(\left( {\frac{2}{7} - x} \right) + \frac{1}{5} = \frac{3}{5}\)

\(\frac{2}{7} - x = \frac{3}{5} - \frac{1}{5}\)

\(\frac{2}{7} - x = \frac{2}{5}\)

\(x = \frac{2}{7} - \frac{2}{5}\)

\(x = \frac{{ - 4}}{{35}}\)

c) \(x + \frac{2}{{3.5}} + \frac{2}{{5.7}} + \frac{2}{{7.9}} = \frac{1}{2}\)

\(x + \frac{1}{3} - \frac{1}{5} + \frac{1}{5} - \frac{1}{7} + \frac{1}{7} - \frac{1}{9} = \frac{1}{2}\)

\(x + \frac{1}{3} - \frac{1}{9} = \frac{1}{2}\)

\(x + \frac{2}{9} = \frac{1}{2}\)

\(x = \frac{1}{2} - \frac{2}{9}\)

\(x = \frac{5}{{18}}\)