(a)
$\left| \begin{matrix}
1 & \log_{x}y & \log_{x}z \\
\log_{y}x & 1 & \log_{y}z \\
\log_{z}x & \log_{z}y & 1
\end{matrix} \right|$
$= 1(1 - \log_{y}{z\log_{z}{y) - \log_{x}{y(\log_{y}x - \log_{z}x\log_{y}{z)}}}}$
$+ \log_{x}z\ (\log_{z}{y\ }\log_{y}x - \log{\ _{z}x})$
$= (1 - \log_{y}{y) - \log_{x}{y\ (\log_{y}{x - \log_{y}{x)}}}}$
$+ \log_{x}{z(\log_{z}{x - \log_{z}{x)}}}$
$= (1 - 1) - 0 + 0 = 0$