0\\\\m^{2}-m-56=0\\\\D=(-1)^{2}-4*(-56)=1+224=225=15^{2} \\\\m_{1}=\frac{1+15}{2}=8\\\\m_{2} =\frac{1-15}{2}=-7" alt="64^{x}-8^{x}-56=0\\\\(8^{x})^{2}-8^{x}-56=0\\\\8^{x}=m,m>0\\\\m^{2}-m-56=0\\\\D=(-1)^{2}-4*(-56)=1+224=225=15^{2} \\\\m_{1}=\frac{1+15}{2}=8\\\\m_{2} =\frac{1-15}{2}=-7" align="absmiddle" class="latex-formula">
m₂ = - 7 - не подходит