Primitive of Reciprocal of a x + b

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Theorem

$\ds \int \frac {\d x} {a x + b} = \frac 1 a \ln \size {a x + b} + C$


Proof

\(\ds \int \frac {\d x} {a x + b}\) \(=\) \(\ds \frac 1 a \int \frac {\map \d {a x + b} } {a x + b}\) Primitive of Function of $a x + b$
\(\ds \) \(=\) \(\ds \frac 1 a \ln \size {a x + b} + C\) Primitive of Reciprocal

$\blacksquare$


Examples

Primitive of $\dfrac 1 {x - a}$

$\ds \int \frac {\d x} {x - a} = \ln \size {x - a} + C$


Sources