Chapter 10: Problem 60
In Exercises, solve for \(x\) or \(t\). $$ e^{-0.5 x}=0.075 $$
Short Answer
Expert verified
The solution to the equation is \(x = 5.1806\).
Step by step solution
01
Apply the natural logarithm to both sides
To remove the base \(e\) from the left-hand-side, apply the natural logarithm \(ln\) to both sides of the given equation. The natural logarithm of a number \(b\), denoted \(ln(b)\), is the power to which \(e\) would have to be raised to equal \(b\). So, applying natural log to both sides, the equation becomes: \[ ln(e^{-0.5 x}) = ln(0.075)\]
02
Use logarithmic identity on the left-hand-side
The natural logarithm of the exponential function is just the function itself. Thereby, \(-0.5x\) is simply left on the left-hand-side: \[-0.5x = ln(0.075)\] The left-hand-side can be rearranged by multiplying by \( -2\), to isolate the variable on the left-hand-side. This results to: \[ x = -2 \times ln(0.075) \].
03
Evaluate the expression
Finally, calculate the value of the right-hand side using a calculator or any computing tool (like Python, Excel, etc.) that allows the computation of the natural logarithm: \[ x = -2 \times -2.5903.\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Exponential Equation
When working with equations, an **exponential equation** is one that sets a constant base raised to a variable in equal standing with a constant or another variable expression.
Exponential equations often involve the base number of mathematics, the natural number \( e \), which is approximately 2.718.
Here, our base \( e \) is raised to the power of \(-0.5x\), with both sides of the equation having to balance: \( e^{-0.5x} = 0.075 \).
Exponential equations often involve the base number of mathematics, the natural number \( e \), which is approximately 2.718.
Here, our base \( e \) is raised to the power of \(-0.5x\), with both sides of the equation having to balance: \( e^{-0.5x} = 0.075 \).
- **Recognize the Base:** The base \( e \) is common in natural growth scenarios and certain mathematical models.
- **Understanding Exponents:** An exponent indicates how many times to multiply the base by itself. Here, we have a negative exponent, which often indicates a division or reciprocal is involved.
- **Solving Approach:** It is critical to isolate the exponents when solving such equations by using logarithms, as exponential growth occurs when a calculation repeatedly applies multiplication.
Solving for a Variable
To **solve for a variable** like \( x \) in an equation, you must effectively isolate the variable on one side of the equation, making its value apparent.
In the given problem, the equation \( e^{-0.5x} = 0.075 \) requires us to remove the exponentiation aspect to help isolate \( x \).
In the given problem, the equation \( e^{-0.5x} = 0.075 \) requires us to remove the exponentiation aspect to help isolate \( x \).
- **Applying the Natural Logarithm:** Taking the natural logarithm on both sides allows you to convert the exponential form to a more straightforward expression.
- **Using the Identity:** The logarithmic identity simplifies the exponent, eliminating the exponential and revealing the multiplication aspect, namely \(-0.5x\).
- **Manipulating the Equation:** By dividing or multiplying all terms, given the coefficient \(-0.5\), you can isolate and solve for the variable \( x \).
Logarithmic Identity
A **logarithmic identity** is a mathematical expression that helps simplify equations involving logarithms.
In the given exercise, we utilize the fact that the natural logarithm \( ln \) of an exponential function with base \( e \) will revert to its exponent.
In the given exercise, we utilize the fact that the natural logarithm \( ln \) of an exponential function with base \( e \) will revert to its exponent.
- **Understanding the Identity:** ln(e^y) = y, which indicates applying the natural log to any base \( e \) exponent returns the exponent itself, simplifying the equation.
- **Application in the Example:** This identity directly translates \( ln(e^{-0.5x}) \) to \( -0.5x \), bypassing the complexity of the exponent.
- **Benefits of the Identity:** It simplifies the steps needed to solve and balances equations that involve natural logarithms instantly.