integral of 1/(x^3-27)

解答

\int \frac{1}{x ^{3} - 27} d x

\frac{1}{27} ln ∣ x - 3 ∣ - \frac{1}{54} ln 4 x^{2} + 12 x + 36 - \frac{1}{9 3} arctan (\frac{2}{3 3} x + \frac{1}{3}) + C

求解步骤

\int \frac{1}{x ^{3} - 27} d x

将

\frac{1}{x ^{3} - 27}

用部份分式展开:

\frac{1}{27 ( x - 3 )} + \frac{- x - 6}{27 ( x ^{2} + 3 x + 9 )}

= \int \frac{1}{27 ( x - 3 )} + \frac{- x - 6}{27 ( x ^{2} + 3 x + 9 )} d x

使用积分加法定则:

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

= \int \frac{1}{27 ( x - 3 )} d x + \int \frac{- x - 6}{27 ( x ^{2} + 3 x + 9 )} d x

\int \frac{1}{27 ( x - 3 )} d x = \frac{1}{27} ln ∣ x - 3 ∣

\int \frac{- x - 6}{27 ( x ^{2} + 3 x + 9 )} d x = \frac{1}{54 3} (- 3 ln 4 x^{2} + 12 x + 36 - 6 arctan (\frac{2}{3 3} x + \frac{1}{3}))

= \frac{1}{27} ln ∣ x - 3 ∣ + \frac{1}{54 3} (- 3 ln 4 x^{2} + 12 x + 36 - 6 arctan (\frac{2}{3 3} x + \frac{1}{3}))

乘开

\frac{1}{54 3} (- 3 ln 4 x^{2} + 12 x + 36 - 6 arctan (\frac{2}{3 3} x + \frac{1}{3})) : - \frac{1}{54} ln 4 x^{2} + 12 x + 36 - \frac{1}{9 3} arctan (\frac{2}{3 3} x + \frac{1}{3})

= \frac{1}{27} ln ∣ x - 3 ∣ - \frac{1}{54} ln 4 x^{2} + 12 x + 36 - \frac{1}{9 3} arctan (\frac{2}{3 3} x + \frac{1}{3})

解答补常数

= \frac{1}{27} ln ∣ x - 3 ∣ - \frac{1}{54} ln 4 x^{2} + 12 x + 36 - \frac{1}{9 3} arctan (\frac{2}{3 3} x + \frac{1}{3}) + C

\int \frac{x ^{3} + 7 x ^{2} + 25 x + 35}{x ^{2} + 5 x + 6} d x

\int \frac{4 sinh ( x )}{4 + cosh ^{2} ( x )} d x

im pl i c i t \frac{d y}{d x}, y = 3 x

\frac{d}{d x} (x + \frac{9}{x})

\int (3 - 8 x) d x