Problem 52 - Intermediate Algebra

Question

Evaluate each expression without using a calculator. $$ \ln e^{-10} $$

Step-by-Step Solution

Answer

-10, because \(\ln(e^{-10}) = -10\).

Step 1: Identify the Expression

We need to evaluate or simplify: \(\ln e^{-10}\).

Step 2: Apply Order of Operations

Following the order of operations (PEMDAS/BODMAS), we simplify the expression step by step, handling parentheses, exponents, multiplication/division, then addition/subtraction.

Step 3: Compute the Result

Carrying out the operations systematically, we arrive at the result.

Step 4: State the Result

-10, because \(\ln(e^{-10}) = -10\).

Key Concepts

Logarithm Rules

Understanding the rules of logarithms can make working with them much easier. A logarithm answers the question: "To what power must we raise the base to obtain a particular number?" For natural logarithms, this base is the irrational number, \(e\).

One of the fundamental rules of logarithms is the power rule: \(\log_b (a^c) = c \cdot \log_b (a)\). This means that if you have a power inside a logarithm, you can bring that exponent outside as a multiplier. Applying this to natural logarithms, \(\ln(e^x) = x\) because the exponent \(x\) is brought in front of \(\ln(e)\), and since \(\ln(e) = 1\) by definition, we are left with just \(x\).

There are other key properties too, like the product rule and the quotient rule, that help simplify complex logarithmic expressions. Understanding these rules can help unravel expressions and facilitate calculations.

Exponential Functions

Exponential functions are a cornerstone of mathematics, often symbolized by \(b^x\), where \(b\) is a constant base and \(x\) is the exponent. With exponential functions, small changes in the exponent can result in large changes in the function's value.

One of the most important exponential functions is \(e^x\), where \(e\) is the aforementioned irrational number. This function is unique because its rate of change is proportional to the value of the function itself, making it prevalent in natural growth processes.

In the context of natural logarithms, the inverse relationship between \(e^x\) and \(\ln\) is crucial. The expression \(\ln(e^x) = x\) highlights this relationship; it shows how the natural log and exponential functions can simplify expressions by effectively "cancelling" each other out.

Irrational Numbers

Irrational numbers are numbers that cannot be expressed as a simple fraction. They have non-repeating, non-terminating decimal expansions. Irrational numbers like \(\pi\) and \(e\) play significant roles in mathematics and science.

Specifically, \(e\) is one of the most famous irrational numbers, valued approximately at 2.71828. It is not merely a mathematical curiosity; \(e\) is essential for calculating continuous growth or decay, such as compound interest or population growth models.

The defining characteristic of natural logarithms is their close relationship with \(e\). When dealing with natural logarithms, recognizing \(e\) as the base provides a powerful tool for simplifying complex mathematical expressions.

• \(\ln(e) = 1\)
• \(\ln(e^x) = x\)

Recognizing and appreciating irrational numbers like \(e\) can deepen your understanding of their role and importance across various mathematical contexts.