\(x-7=a;\text{ }x-8=b\)
\(a^4+b^4=\left(a+b\right)^4\)
\(\Leftrightarrow a^4+b^4=a^4+b^4+4ab\left(a^2+b^2\right)+6a^2b^2\)
\(\Leftrightarrow2ab\left(2a^2+2b^2+3ab\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}ab=0\\2\left(a+\frac{3b}{4}\right)^2+\frac{7}{8}b^2\end{cases}=0}\)
\(\Leftrightarrow\orbr{\begin{cases}ab=0\\a=b=0\end{cases}}\)