Tìm x, biết: a) 2/5 + 3/5x = 0
Giải thích
a) \[\frac{2}{5} + \frac{3}{5}x = 0\]
\[\frac{3}{5}x = - \frac{2}{5}\]
\[x = \frac{{ - 2}}{5}:\frac{3}{5}\]
\[x = \frac{{ - 2}}{5} \cdot \frac{5}{3}\]
\[x = \frac{{ - 2}}{3}.\]
Vậy \[x = \frac{{ - 2}}{3}.\]
b) \(0,2 - 0,8:x = 0,15\)
\(0,8:x = 0,2 - 0,15\)
\(0,8:x = 0,05\)
\(x = 0,8:0,05\)
\(x = 16\)
Vậy \(x = 16.\)
c) \(\frac{1}{3}:x + \left( { - \frac{3}{4} + \frac{2}{3}} \right):x = \frac{5}{8}\)
\(\frac{1}{3} \cdot \frac{1}{x} - \frac{1}{{12}} \cdot \frac{1}{x} = \frac{5}{8}\)
\(\left( {\frac{1}{3} - \frac{1}{{12}}} \right) \cdot \frac{1}{x} = \frac{5}{8}\)
\(\frac{1}{4} \cdot \frac{1}{x} = \frac{5}{8}\)
\(\frac{1}{x} = \frac{5}{2}\)
\(x \cdot 5 = 1 \cdot 2\)
\(5x = 2\)
\(x = \frac{2}{5}\)
Vậy \(x = \frac{2}{5}.\)