Tìm x biết: a) 1 1/5 + 4/5 : x= 0,75

a) \[1\frac{1}{5} + \frac{4}{5}:x = 0,75\]

\[\frac{6}{5} + \frac{4}{5}:x = \frac{3}{4}\]

\[\frac{4}{5}:x = \frac{{ - 9}}{{20}}\]

\[x = \frac{{ - 16}}{9}.\]

Vậy \[x = \frac{{ - 16}}{9}.\]

b) \(\frac{1}{9} \cdot {3^4} \cdot {3^x} = {3^7}\)

\({3^2} \cdot {3^x} = {3^7}\)

\({3^x} = {3^5}\)

\(x = 5\)

Vậy \(x = 5.\)

c) \({\left( {x + \frac{1}{2}} \right)^2} = \frac{1}{{16}}\)

Suy ra \(x + \frac{1}{2} = \frac{1}{4}\) hoặc \(x + \frac{1}{2} = \frac{{ - 1}}{4}\).

Vậy \(x \in \left\{ {\frac{{ - 3}}{4};\frac{{ - 1}}{4}} \right\}.\)