5.8 Integrals of the inverse of a linear function

The integral I =\mathop{ \mathop{\mathop{∫ }\nolimits }}\nolimits (1)∕(ax + b)\kern 1.66702pt dx, can be done by substitution, z = ax + b, dx = dz∕a, I = {1\over a}\mathop{ \mathop{\mathop{∫ }\nolimits }}\nolimits {1\over z}\kern 1.66702pt dz = {1\over a}(\mathop{ln}\nolimits z + C). Thus

\class{boxed}{ I =\mathop{ \mathop{\mathop{∫ }\nolimits }}\nolimits (1)∕(ax + b)\kern 1.66702pt dx = {1\over a}\left (\mathop{ln}\nolimits (ax + b) + C\right . }