Problem 92 - Precalculus

Question

Determine whether each statement is true or false. \(e^{x}=-2\) has no solution.

Step-by-Step Solution

Answer

True. The statement is true since \(e^x\) cannot be negative.

Step 1: Understanding the Properties of Exponential Functions

The exponential function, denoted as \(e^x\), is defined for all real numbers \(x\). Its range includes all positive real numbers (greater than zero). Therefore, \(e^x\) can never be negative, such as \(-2\).

Step 2: Verifying the Given Statement

According to the nature of the exponential function, \(e^x = -2\) does not have a solution since the exponential function cannot output a negative value. This implies that there is no real number \(x\) for which \(e^x = -2\).

Step 3: Concluding the Truthfulness of the Statement

Since there is no real number \(x\) that satisfies \(e^x = -2\), the given statement, "\(e^x = -2\) has no solution" is indeed true.

Key Concepts

Properties of Exponential Functions

Exponential functions are fascinating mathematical entities characterized by the expression \(e^x\), where \(e\) is a mathematical constant approximately equal to 2.718. These functions have some distinct properties that set them apart from other types of functions.

• Continuous and Smooth: Exponential functions are continuous, which means there are no gaps or jumps. They are also smooth, possessing sleek, unbroken curves.
• Always Positive: The value of an exponential function \(e^x\) is always positive for all real numbers \(x\). This means it never crosses or even touches the x-axis.
• Growth and Decay: They exhibit rapid growth as \(x\) increases and rapid decay as \(x\) becomes negative. The rate of change is proportional to their value, leading to exponential growth or decay.
• Horizontal Asymptote: As \(x\) approaches negative infinity, \(e^x\) approaches zero, but it never actually reaches zero.

These properties define the behavior of exponential functions and ensure that their output values remain strictly positive.

Range of Exponential Functions

The range of an exponential function like \(e^x\) is an essential aspect to understand. It's crucial in recognizing why certain equations have no solutions. The range of \(e^x\) is all positive real numbers. This concept can be understood by imagining the x-axis as the point at which \(e^x\) approaches but never touches or crosses. Since \(e^x\) constantly outputs values greater than zero, it means you can't obtain a negative number or zero from this function. Therefore, when faced with an equation such as \(e^x = -2\), it becomes clear why it is impossible to find a real \(x\) that satisfies this condition; because -2 is not within the range of \(e^x\). Appling this understanding simplifies many problems involving exponential equations.

Solving Exponential Equations

Solving exponential equations involves finding the value of \(x\) that makes the equation true. For many exponential equations, understanding the properties and range is key. Consider an equation of the form \(e^x = a\), where \(a\) is a real number.

• Solutions Only for Positive Values: If \(a > 0\), we can find a solution by taking the natural logarithm to find \(x = \ln(a)\).
• No Real Solutions for Non-Positive Values: If \(a \leq 0\), there are no real solutions. The exponential function does not produce non-positive values, aligning with our earlier discussion on its range.

When working on exponential equations, always consider if the given value \(a\) falls within the range of the exponential function, i.e., positive real numbers. If not, then the equation does not have real solutions.