Как решать подобные примеры? ( 13 вариант )

[latex]\\ \left ( {3\over7} \right )^{3-2x}=\left ( {49\over9} \right )^{-3}\\\\ \left ( {3\over7} \right )^{3-2x}=\left ( ({3\over7})^{-2} \right )^{-3}\\\\ \left ( {3\over7} \right )^{3-2x}=\left ( {3\over7} \right )^{6}\\\\ 3-2x=6\\ 2x=-3\\ x=-1,5\\\\\\[/latex] [latex]\\\\[/latex] [latex]\\ \left ( {51\over9} \right )^{71\sqrt{x-1}-3}=\left ( {9\over51} \right )^{3\sqrt{x-1}-293}\\\\ \left ( {9\over51} \right )^{-71\sqrt{x-1}+3}=\left ( {9\over51} \right )^{3\sqrt{x-1}-293}\\\\ -71\sqrt{x-1}+3=3\sqrt{x-1}-293\\ 74\sqrt{x-1}=296\\ \sqrt{x-1}=4\\ x-1=16\\ x=17\\[/latex] [latex]\\ 6*5^{-2x+3}-1=5^{-x+1}\\ 6*5^3*5^{-2x}-1=5*5^{-x}\\ t=5^{-x}(t>0)\\ 5^3*6t^2-1=5t\\ 5^3*6t^2-5t-1=0\\ D+25+24*125=3025\\ t_1={5+\sqrt{3025}\over 250*6}={1\over25}\\ t_1={5-\sqrt{3025}\over 250*6}=-{1\over30}\\\\ 5^{-x}={1\over25}, x=2\\ 5^{-x}=-{1\over30}, x\in\varnothing\\[/latex]