0\\\\5x-4>0\\\\x>0,8\\\\lg(5x-4)\neq0\\\\5x-4\neq1\\\\x\neq1\\\\x\in(0,8;1)u(1;+\infty)\\\\2lgx=lg(5x-4)\\\\lgx^{2}=lg(5x-4)\\\\x^{2}=5x-4\\\\x^{2}-5x+4=0\\\\x_{1}=4\\\\x_{2} =1" alt="3)\frac{2lgx}{lg(5x-4)}=1\\\\x>0\\\\5x-4>0\\\\x>0,8\\\\lg(5x-4)\neq0\\\\5x-4\neq1\\\\x\neq1\\\\x\in(0,8;1)u(1;+\infty)\\\\2lgx=lg(5x-4)\\\\lgx^{2}=lg(5x-4)\\\\x^{2}=5x-4\\\\x^{2}-5x+4=0\\\\x_{1}=4\\\\x_{2} =1" align="absmiddle" class="latex-formula">
x = 1 - посторонний корень
Ответ : 4