0\\2t^2-t-1=0\\D=1+4\cdot2=9\\t_{1,2}=\frac{1\pm3}4\\t_1=-\frac12\;-\;He\;nogx.\\t_2=1\\5^x=1\Rightarrow x=0\\\\\\4^{x-1}+4^x+4^{x+1}=84\\\frac14\cdot4^x+4^x+4\cdot4^x=84\\\frac{21}44^x=84\\4^x=84:\frac{21}4=84\cdot\frac4{21}=4\cdot4=4^2\\x=2" alt="2\cdot5^{2x}=5^x+1\\2\cdot5^{2x}-5^x-1=0\\5^x=t,\;5^{2x}=t^2,\;t>0\\2t^2-t-1=0\\D=1+4\cdot2=9\\t_{1,2}=\frac{1\pm3}4\\t_1=-\frac12\;-\;He\;nogx.\\t_2=1\\5^x=1\Rightarrow x=0\\\\\\4^{x-1}+4^x+4^{x+1}=84\\\frac14\cdot4^x+4^x+4\cdot4^x=84\\\frac{21}44^x=84\\4^x=84:\frac{21}4=84\cdot\frac4{21}=4\cdot4=4^2\\x=2" align="absmiddle" class="latex-formula">