Primitive of Reciprocal of Root of a x squared plus b x plus c

Theorem
Let $a \in \R_{\ne 0}$.

Then:
 * $\displaystyle \int \frac {\mathrm d x} {\sqrt {a x^2 + b x + c} } = \begin{cases}

\dfrac 1 {\sqrt a} \ln \left({2 \sqrt a \sqrt {a x^2 + b x + c} + 2 a x + b}\right) + C & : b^2 - 4 a c > 0 \\ \dfrac 1 {\sqrt a} \sinh^{-1} \left({\dfrac {2 a x + b} {\sqrt{4 a c - b^2} } }\right) + C & : b^2 - 4 a c < 0 \\ \dfrac 1 {\sqrt a} \ln \left\vert{2 a x + b}\right\vert + C & : b^2 - 4 a c = 0 \end{cases}$

Proof
First:

Put:

Let $D = b^2 - 4 a c$.

Thus: