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Ch. 8 - Techniques of Integration
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 8, Problema 8.5.60

Use any method to evaluate the integrals in Exercises 55–66.
∫ (x⁴ - 1) / (x⁵ - 5x + 1) dx

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First, examine the integral \( \int \frac{x^{4} - 1}{x^{5} - 5x + 1} \, dx \) and consider if the numerator is related to the derivative of the denominator. This is a common strategy for integrals involving rational functions.
Compute the derivative of the denominator: \( \frac{d}{dx} (x^{5} - 5x + 1) = 5x^{4} - 5 \).
Notice that the numerator \( x^{4} - 1 \) is similar to \( \frac{1}{5} \) times the derivative of the denominator, since \( 5x^{4} - 5 = 5(x^{4} - 1) \). This suggests rewriting the integral in terms of \( \frac{f'(x)}{f(x)} \) where \( f(x) = x^{5} - 5x + 1 \).
Rewrite the integral as \( \int \frac{x^{4} - 1}{x^{5} - 5x + 1} \, dx = \int \frac{1}{5} \cdot \frac{5x^{4} - 5}{x^{5} - 5x + 1} \, dx = \frac{1}{5} \int \frac{f'(x)}{f(x)} \, dx \).
Use the formula \( \int \frac{f'(x)}{f(x)} \, dx = \ln|f(x)| + C \) to express the integral in terms of the natural logarithm of the denominator, multiplied by the constant factor \( \frac{1}{5} \).

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