integral of (x^3)/(x^2-x-6)

解答

\int \frac{x ^{3}}{x ^{2} - x - 6} d x

\frac{x ^{2}}{2} + x + 14 (\frac{1}{4} ln 4 x^{2} - 4 x - 24 - \frac{1}{20} (ln \frac{4}{5} + \frac{2}{5} x - ln - \frac{6}{5} + \frac{2}{5} x)) + 6 (- \frac{1}{5} ln ∣ x + 2 ∣ + \frac{1}{5} ln ∣ x - 3 ∣) + C

求解步骤

\int \frac{x ^{3}}{x ^{2} - x - 6} d x

分解

\frac{x ^{3}}{x ^{2} - x - 6}

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

长除

\frac{x ^{3}}{( x + 2 ) ( x - 3 )} : x + 1 + \frac{7 x + 6}{x ^{2} - x - 6}

= \int x + 1 + \frac{7 x + 6}{x ^{2} - x - 6} 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 x d x + \int 1 d x + \int \frac{7 x + 6}{x ^{2} - x - 6} d x

\int x d x = \frac{x ^{2}}{2}

\int 1 d x = x

\int \frac{7 x + 6}{x ^{2} - x - 6} d x = 14 (\frac{1}{4} ln 4 x^{2} - 4 x - 24 - \frac{1}{20} (ln \frac{4}{5} + \frac{2}{5} x - ln - \frac{6}{5} + \frac{2}{5} x)) + 6 (- \frac{1}{5} ln ∣ x + 2 ∣ + \frac{1}{5} ln ∣ x - 3 ∣)

= \frac{x ^{2}}{2} + x + 14 (\frac{1}{4} ln 4 x^{2} - 4 x - 24 - \frac{1}{20} (ln \frac{4}{5} + \frac{2}{5} x - ln - \frac{6}{5} + \frac{2}{5} x)) + 6 (- \frac{1}{5} ln ∣ x + 2 ∣ + \frac{1}{5} ln ∣ x - 3 ∣)

解答补常数

= \frac{x ^{2}}{2} + x + 14 (\frac{1}{4} ln 4 x^{2} - 4 x - 24 - \frac{1}{20} (ln \frac{4}{5} + \frac{2}{5} x - ln - \frac{6}{5} + \frac{2}{5} x)) + 6 (- \frac{1}{5} ln ∣ x + 2 ∣ + \frac{1}{5} ln ∣ x - 3 ∣) + C

\int \frac{7 x ^{2} - x - 5}{x ^{2} - 1} d x

\int \frac{x ^{3}}{3 1 - 4 x ^{2}} d x

\int \frac{1}{x 4 x + 81} d x

\int \frac{( 5 x - 3 ) ^{3}}{x ^{3}} d x

\int - 2 π sin^{2} (2 x) d x