Tìm \(x,\) biết: a) \(\frac{9}{{12}} - x = - \frac{3}{5}.\) b) \(0,2 + 0,8:x = 0,15.\) c) \[\left( {5 + 4x} \right)\left( {\frac{5}{4}x - 2} \right) = 0
Giải thích
a) \(\frac{9}{{12}} - x = - \frac{3}{5}\)
\(x = \frac{9}{{12}} - \left( { - \frac{3}{5}} \right)\)
\(x = \frac{3}{4} + \frac{3}{5}\)
\(x = \frac{{27}}{{20}}\)
Vậy \(x = \frac{{27}}{{20}}.\)
b) \(0,2 + 0,8:x = 0,15\)
\(0,8:x = 0,15 - 0,2\)
\(0,8:x = - 0,05\)
\(x = 0,8:\left( { - 0,05} \right)\)
\(x = - 16\)
Vậy \(x = - 16.\)
c) \(\left( {5 + 4x} \right)\left( {\frac{5}{4}x - 2} \right) = 0\)
\[5 + 4x = 0\] hoặc \(\frac{5}{4}x - 2 = 0\)
Trường hợp 1:
\[5 + 4x = 0\]
\(4x = - 5\)
\(x = - \frac{5}{4}\)
Trường hợp 2:
\(\frac{5}{4}x - 2 = 0\)
\(\frac{5}{4}x = 2\)
\(x = 2:\frac{5}{4}\)
\(x = \frac{8}{5}.\)Vậy \(x \in \left\{ { - \frac{5}{4};\,\,\frac{8}{5}} \right\}.\)