integral of 1/(x(x+1)(x+3))

解

\int \frac{1}{x ( x + 1 ) ( x + 3 )} d x

\frac{1}{3} ln ∣ x ∣ - \frac{1}{2} ln ∣ x + 1 ∣ + \frac{1}{6} ln ∣ x + 3 ∣ + C

解答ステップ

\int \frac{1}{x ( x + 1 ) ( x + 3 )} d x

以下の部分分数を得る:

\frac{1}{x ( x + 1 ) ( x + 3 )} : \frac{1}{3 x} - \frac{1}{2 ( x + 1 )} + \frac{1}{6 ( x + 3 )}

= \int \frac{1}{3 x} - \frac{1}{2 ( x + 1 )} + \frac{1}{6 ( x + 3 )} d x

総和規則を適用する:

\int f (x) \pm g (x) d x = \int f (x) d x \pm \int g (x) d x

= \int \frac{1}{3 x} d x - \int \frac{1}{2 ( x + 1 )} d x + \int \frac{1}{6 ( x + 3 )} d x

\int \frac{1}{3 x} d x = \frac{1}{3} ln ∣ x ∣

\int \frac{1}{2 ( x + 1 )} d x = \frac{1}{2} ln ∣ x + 1 ∣

\int \frac{1}{6 ( x + 3 )} d x = \frac{1}{6} ln ∣ x + 3 ∣

= \frac{1}{3} ln ∣ x ∣ - \frac{1}{2} ln ∣ x + 1 ∣ + \frac{1}{6} ln ∣ x + 3 ∣

定数を解答に追加する

= \frac{1}{3} ln ∣ x ∣ - \frac{1}{2} ln ∣ x + 1 ∣ + \frac{1}{6} ln ∣ x + 3 ∣ + C