Answer
See below.
Work Step by Step
We know that $\log_a1=0$ and that $\log_a x+\log_a y=log_a (x\cdot y)$, hence $\log_a{(x+\sqrt{x^2-1})}+\log_a{(x-\sqrt{x^2-1})}=\log_a{(x+\sqrt{x^2-1})(x-\sqrt{x^2-1})}=\log_a{(x^2-(x^2-1))}=\log_a{1}=0$
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