Question

Write the logarithm in terms of natural logarithms.\(\log _{1 / 5} x\)

Short answer

\(\log _{1/5} x = \frac{ln x}{ln (1/5)}\)

Step-by-step solution

Identify the given logarithm

We are given the logarithm \(\log _{1/5} x\)

Apply the change of base formula

The change of base formula is \(log _b a = \frac{log _d a}{log _d b}\). We can use this formula to rewrite our logarithm in terms of the natural logarithm (base e). Substitute \(a = x\), \(b = 1/5\), and \(d = e\) (base of the natural logarithm), into the formula, we get: \(\log _{1/5} x = \frac{log _e x}{log _e (1/5)}\).

Simplify the equation

In mathematics, the natural logarithm is usually written as ln, so the equation can be simplified as: \(\log _{1/5} x = \frac{ln x}{ln (1/5)}\).

Key concepts

Natural Logarithms

The natural logarithm, denoted as 'ln', is a special type of logarithm where the base is the mathematical constant 'e', approximately equal to 2.71828. Natural logarithms are fundamental in various aspects of mathematics, particularly in calculus because the derivative of the natural logarithm function, which is \( \frac{d}{dx} \ln(x) = \frac{1}{x} \), exhibits a simple form that makes computation easier.

Understanding natural logarithms is vital for students tackling growth and decay problems, as well as complex financial calculations. They are also intrinsic to Euler's identity and are used to solve differential equations. In our exercise, the natural logarithm helps to convert a logarithm of base \( \frac{1}{5} \) into a more common and calculable form.

Logarithmic Identities

Logarithmic identities are tools that make it easier to work with logarithms. They are the properties that allow us to manipulate logarithmic expressions and solve various logarithmic equations. Some key logarithmic identities include:

• Product Identity: \( \log_b(mn) = \log_b(m) + \log_b(n) \)
• Quotient Identity: \( \log_b(\frac{m}{n}) = \log_b(m) - \log_b(n) \)
• Power Identity: \( \log_b(m^k) = k \log_b(m) \)

These identities reflect how logarithms interact with multiplication, division, and exponents, respectively. In our textbook problem, we employed the change of base formula—a critical logarithmic identity that enables the evaluation of logarithms with bases other than 'e' or 10 by expressing them in terms of logarithms with a convenient base.

Solving Logarithmic Equations

Solving logarithmic equations often involves isolating the logarithmic expression and utilizing properties of logarithms to simplify the equation. Steps to solve logarithmic equations may include:

• Combining or separating logs using logarithmic identities
• Converting the logarithmic equation into an exponential form, because logarithms are the inverse functions of exponentials
• Applying the change of base formula to work within a common base for more straightforward calculation

It is also crucial to watch for extraneous solutions, as not all values will satisfy the original logarithmic equation. For instance, in our problem, after simplifying the expression using the change of base formula, additional steps may be needed to solve for 'x' if it were set to a specific value. Ultimately, understanding how to manipulate these equations is essential for finding accurate solutions in diverse mathematical fields.