Spiegel's "Mathematical Handbook of Formulas and Tables" (Schaum, 1968), item $14.655$ gives:
$$\int \frac {\cosh^{-1} (x/a) \, \mathrm d x} {x^2} = \dfrac {-\cosh^{-1} (x/a) } x \mp \dfrac 1 a \ln \left({\dfrac {a + \sqrt {x^2 + a^2} } x}\right)$$
(negative for $\cosh^{-1} (x/a) > 0$, positive for $\cosh^{-1} (x/a) < 0$)
Let's ignore the fact for now that $\cosh^{-1}$ is AFAIK defined as being the $+$ve branch of the function, and roll with what we've got.
It is assumed at this stage that $a > 0$.
Integration by parts:
$u = \cosh^{-1} (x/a) \implies \dfrac {\mathrm d u} {\mathrm d x} = \dfrac 1 {\sqrt {x^2 - a^2} }$
$\dfrac {\mathrm d v} {\mathrm d x} = \dfrac 1 {x^2} \implies v = \dfrac {-1} x$
allows us to assemble:
$$ \int \frac {\cosh^{-1} (x/a) \,\mathrm d x} {x^2} = \frac {-\cosh^{-1} (x/a)} x + \int \frac {\mathrm d x} {x \sqrt {x^2 - a^2} } + C$$
But then we've got this standard integral:
$$\int \frac {\mathrm d x} {x \sqrt {x^2 - a^2} } = \frac 1 a \operatorname {arcsec} \left|{\frac x a}\right| + C$$
In order to return to Spiegel's result, the denominator of the integrand on the RHS of the above would need to be $\displaystyle \int \dfrac {\mathrm d x} {x \sqrt {a^2 - x^2} }$.
But I can't work out how to make it be so. The derivative of $\cosh^{-1} (x/a)$ is pretty well established as being $\dfrac 1 {\sqrt {x^2 - a^2} }$, and you would expect this to be the case, as $\cosh^{-1}$ is defined only on $x > a$ in the first place.
Am I correct in assuming that Spiegel has made a mistake?
