Primitive of Reciprocal of x by x fourth plus a fourth
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Theorem
- $\ds \int \frac {\d x} {x \paren {x^4 + a^4} } = \frac 1 {4 a^4} \map \ln {\frac {x^4} {x^4 + a^4} }$
Proof
From Primitive of Reciprocal of x by Power of x plus Power of a:
- $\ds \int \frac {\d x} {x \paren {x^n + a^n} } = \frac 1 {n a^n} \ln \size {\frac {x^n} {x^n + a^n} } + C$
So:
\(\ds \int \frac {\d x} {x \paren {x^4 + a^4} }\) | \(=\) | \(\ds \frac 1 {4 a^4} \ln \size {\frac {x^4} {x^4 + a^4} } + C\) | Primitive of $\dfrac 1 {x \paren {x^n + a^n} }$ with $n = 4$ | |||||||||||
\(\ds \) | \(=\) | \(\ds \frac 1 {4 a^4} \map \ln {\frac {x^4} {x^4 + a^4} } + C\) | Absolute Value of Even Power |
directly.
$\blacksquare$
Sources
- 1968: Murray R. Spiegel: Mathematical Handbook of Formulas and Tables ... (previous) ... (next): $\S 14$: Integrals involving $x^4 \pm a^4$: $14.315$