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Integrate[1/(x*Sqrt[-a^2 + x^2]), x] ==
((-I)*Log[(2*((-I)*a + Sqrt[-a^2 + x^2]))/x])/a

                 1
Integrate[----------------, x] == 
                   2    2
          x Sqrt[-a  + x ]

                        2    2
       2 (-I a + Sqrt[-a  + x ])
-I Log[-------------------------]
                   x
---------------------------------
                a