Реши уравнения

а) \(\left(\dfrac{1}{3}\right)^x=9\) ; \(x=\) [ ];

б) \(2^{2x-7}=8\) ; \(x=\) [ ];

в) \(\log\_2 x=3\) ; \(x=\) [ ];

г) \(\log\_\frac{1}{2} (3x+1)=-2\) ; \(x=\) [ ].