Question

Use a graphing calculator to solve the equation.\(\ln 2 x=3^{-x+2}\)

Short answer

The solution to the equation is the x-value of the intersection point of the two graphs, which is obtained using a graphing calculator. The exact value can vary depending on the calculator used.

Step-by-step solution

Input the Functions

First, we need to input the two sides of the equation as separate functions in the graphing calculator. The first function is \(y_1 = \ln 2x\) and the second function is \(y_2 = 3^{-x+2}\).

Draw the Graphs

After throwing in the two functions, we proceed to sketch the graphs corresponding to these functions. It becomes apparent that the solution to the equation is the x-coordinate of the intersection point of these graphs.

Find the Intersection

In most graphing calculators, there is a function called “intersection” under the 'calculate' menu, which we can use to find the intersection point of these two graphs. We need to follow the calculator’s directions to get to this point. After obtaining the intersection, the x-coordinate of this point represents the solution to our equation.

Key concepts

Logarithmic Functions

Logarithmic functions are an essential part of understanding many mathematical and real-world phenomena. These functions have the form \(y = \log_b(x)\), where \(b\) is the base of the logarithm. In our exercise, we focus on the natural logarithm, denoted as \(\ln x\), which uses the base \(e \approx 2.718\). Logarithmic functions are the inverse of exponential functions, making them particularly useful for solving equations where the variable appears as an exponent.

Key properties of logarithmic functions include:

• If \(y = \ln x\), then \(x = e^y\).
• The natural logarithm of 1 is 0, i.e., \(\ln 1 = 0\).
• The function is undefined for \(x \leq 0\).

These properties help simplify complex equations, especially when dealing with exponential growth or decay in fields such as biology, finance, and physics. For our equation, \(\ln 2x\), the function represents the natural logarithm of \(2x\) and is graphed as part of the solution-finding process.

Exponential Functions

Exponential functions are characterized by their constant rate of growth or decay. They have the general form \(y = a^{x}\), where \(a\) is a positive constant, known as the base. These functions are widely used to model populations, radioactive decay, and financial growth, among other phenomena.

In the exercise, the function \(3^{-x+2}\) is exponential, where the base is 3, and the power involves the variable \(x\). Understanding exponential functions is crucial for solving equations where one or more variables appear in the exponent. Key traits include:

• They pass through the point \((0,1)\) if the base is not modified by any additional constants.
• Exponential growth occurs when the base is greater than 1; decay happens when it is between 0 and 1.
• The function is continuous and has a horizontal asymptote, typically the x-axis.

This exponential function assists in setting up the graph to find where it intersects with the logarithmic function, thereby aiding the solution to the equation.

Equation Solving

The process of equation solving involves finding the value(s) of the variable(s) that satisfy the equation. In this exercise, we use a graphing calculator to solve the equation \(\ln 2x = 3^{-x+2}\). Using a graphing calculator simplifies solving complex equations visually, especially when symbolic solutions are challenging or impossible.

Here's how it typically works:

• Input each side of the equation as separate functions, \(y_1 = \ln 2x\) and \(y_2 = 3^{-x+2}\).
• Graph these functions to visualize where they intersect.
• Use the calculator's intersection feature to locate the exact point of intersection, which provides the solution for \(x\).

This intersection method enables students to understand how the graphical representation of equations can lead to finding solutions numerically. Furthermore, it bridges the gap between algebraic and graphical approaches to equation solving, thereby integrating different concepts seamlessly.