7. Given real numbers $a, b, c, d$ satisfy $5^{a}=4,4^{b}=3,3^{c}=2,2^{d}=5$, then $(a b c d)^{2018}=$
Rong's Problem 1.
Parse $5^{a}=4,4^{b}=3,3^{c}=2,2^{d}=5$ into logarithms, we have $a=\log _{5} 4=\frac{\ln 4}{\ln 5}, b=\frac{\ln 3}{\ln 4}, c=\frac{\ln 2}{\ln 3}, d=\frac{\ln 5}{\ln 2}$, so
$$
(a b c d)^{2018}=\left(\frac{\ln 4}{\ln 5} \times \frac{\ln 3}{\ln 4} \times \frac{\ln 2}{\ln 3} \times \frac{\ln 5}{\ln 2}\right)^{2018}=1^{2018}=1
$$