We'll recall the formula of integrating by
parts:
Int udv = u*v - Int
vdu
Let u = (ln x)^2 => du = 2*ln x
dx/x
Let dv = dx/x^2 => v =
-1/x
Int (ln x)^2 dx/x^2 = -(ln x)^2/x + 2 Int (ln x)
dx/x^2 (*)
We'll integrate by parts again the integral Int
(ln x) dx/x^2:
Let u = (ln x) => du =
dx/x
Let dv = dx/x^2 => v =
-1/x
Int (ln x) dx/x^2 = -(ln x)/x + Int
dx/x^2
Int (ln x) dx/x^2 = -(ln x)/x - 1/x + C
(**)
We'll replace (**) in
(*):
Int (ln x)^2 dx/x^2 = -(ln x)^2/x + 2*[-(ln x)/x -
1/x] + C
Int (ln x)^2 dx/x^2 = -[(ln x)^2 +
(ln (x^2)) + 2]/x + C
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