'Find all number `a`for which each of the following equalities hold true? (a) `(log)_1a=2` (b)

"Find all number `a`
for which each of the following equalities hold true?
(a) `(log)_1a=2`
(b) `(log)_(10)(a(a+3))=1`
(c) `log_(1//3)(a^2-1)=-1`
(d) `(log)_2(a^2-5)=2`"

`(log)_1a=2`