let
x= atanu
dx = a(secu)^2 .du
∫√(x^2+a^2)/x^2 dx
=∫ [(asecu)/(atanu)^2] .[a(secu)^2 .du]
=∫ (secu)^3/(tanu)^2 du
=∫ du/ [(sinu)^2.cosu ]
=∫ [cosu/(sinu)^2 + 1/cosu ] du
=∫ cosu/(sinu)^2 du + ln|secu + tanu|
=∫ dsinu/(sinu)^2 + ln|secu + tanu|
=-1/sinu + ln|secu + tanu| + C
=-√(x^2+a^2)/x + ln| √(x^2+a^2) /a + x/a | + C