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Ch. 3 - Derivatives
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 3, Problema 3.9.82

75–86. Logarithmic differentiation Use logarithmic differentiation to evaluate f'(x).
f(x) = x⁸cos³ x / √x-1

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Step 1: Begin by taking the natural logarithm of both sides of the equation. This will help simplify the differentiation process. Write: ln(f(x)) = ln(x⁸cos³(x)/√(x-1)).
Step 2: Use the properties of logarithms to break down the expression. Apply the logarithm rules: ln(a/b) = ln(a) - ln(b) and ln(a^b) = b*ln(a). This gives: ln(f(x)) = 8ln(x) + 3ln(cos(x)) - (1/2)ln(x-1).
Step 3: Differentiate both sides with respect to x. Remember that the derivative of ln(f(x)) is (1/f(x)) * f'(x). For the right side, differentiate each term separately: d/dx[8ln(x)] = 8/x, d/dx[3ln(cos(x))] = -3sin(x)/cos(x), and d/dx[-(1/2)ln(x-1)] = -(1/2)/(x-1).
Step 4: Combine the derivatives from Step 3 to find the expression for f'(x)/f(x). This results in: f'(x)/f(x) = 8/x - 3tan(x) - 1/(2(x-1)).
Step 5: Solve for f'(x) by multiplying both sides by f(x). This gives: f'(x) = f(x) * (8/x - 3tan(x) - 1/(2(x-1))). Substitute f(x) = x⁸cos³(x)/√(x-1) back into the equation to express f'(x) in terms of x.

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Logarithmic Differentiation

Logarithmic differentiation is a technique used to differentiate complex functions by taking the natural logarithm of both sides. This method simplifies the differentiation process, especially for products, quotients, or powers, by transforming multiplicative relationships into additive ones. It is particularly useful when dealing with functions that involve variable exponents or products of functions.
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