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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 7, Problem 7.3.71

In Exercises 59–86, find the derivative of y with respect to the given independent variable.
71. y = log₂(5θ)

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1
Recall the formula for the derivative of a logarithm with an arbitrary base: if \( y = \log_a(u) \), then \( \frac{dy}{dx} = \frac{1}{u \ln(a)} \cdot \frac{du}{dx} \), where \( \ln \) is the natural logarithm.
Identify the base \( a \) and the argument \( u \) in the given function. Here, \( y = \log_2(5\theta) \), so \( a = 2 \) and \( u = 5\theta \).
Compute the derivative of the inside function \( u = 5\theta \) with respect to \( \theta \). Since \( 5 \) is a constant, \( \frac{du}{d\theta} = 5 \).
Apply the derivative formula: \( \frac{dy}{d\theta} = \frac{1}{5\theta \ln(2)} \times 5 \).
Simplify the expression by canceling common factors if possible to express the derivative in its simplest form.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Derivative of Logarithmic Functions

The derivative of a logarithmic function depends on its base. For a logarithm with base a, log_a(x), the derivative is 1/(x ln(a)) times the derivative of x. Understanding this allows you to differentiate log₂(5θ) by applying the chain rule.
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Derivative of the Natural Logarithmic Function

Chain Rule

The chain rule is used to differentiate composite functions. When a function is inside another, like 5θ inside the logarithm, you first differentiate the outer function with respect to the inner function, then multiply by the derivative of the inner function.
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Intro to the Chain Rule

Properties of Logarithms

Logarithmic properties, such as log_a(bx) = log_a(b) + log_a(x), can simplify differentiation. Recognizing these properties helps break down complex logarithmic expressions into simpler parts, making differentiation more straightforward.
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Change of Base Property