7.299 A=\frac{1-\log _{1 / a} \frac{1}{(a-b)^{2}}+\log _{a}^{2}(a-b)}{\left(1-\log _{\sqrt{a}}(a-b)+\log _{a}^{2}(a-b)\right)^{\frac{1}{2}}}
$$

7.299 A=\frac{1-\log _{1 / a} \frac{1}{(a-b)^{2}}+\log _{a}^{2}(a-b)}{\left(1-\log _{\sqrt{a}}(a-b)+\log _{a}^{2}(a-b)\right)^{\frac{1}{2}}}
$$
Solution. $A=\frac{1-2 \log _{a}(a-b)+\log _{a}^{2}(a-b)}{\left(1-2 \log _{a}(a-b)+\log _{a}^{2}(a-b)\right)^{\frac{1}{2}}}=\frac{\left(1-\log _{a}(a-b)\right)^{2}}{\left|1-\log _{a}(a-b)\right|}$.

1) $\log _{a}(a-b)-1>0$, if $\left\{\begin{array}{l}a>1, \\ b1, \\ 01, \\ b 1 , } \\
{ 0 < b < a }
\end{array} \text { or } \left\{\begin{array}{l}
0<a<1, \\
b<0 .
\end{array}\right.\right.
$