Math Problem Statement

Show that the equation has three unique solutions by using the following steps: i. Define a function that has zeros whenever the given equation has a solution. ii. Provide a plot of the graph and indicate approximate locations of three of the function’s zeros. (desmos.com might be helpful for this!) iii. Use the Intermediate Value Theorem to show that there actually is three zeros near the ones you found by plotting. Make sure you verify all necessary conditions for the Intermediate Value Theorm to apply. x tan(x) = 2^ x − x^2/3

f (x) y = f (x)

Solution

To show that the equation xtan(x)=2xx23x \tan(x) = 2^x - \frac{x^2}{3} has three unique solutions, we will follow the outlined steps:


Step i. Define a function that has zeros whenever the given equation has a solution:

The given equation is:

xtan(x)=2xx23x \tan(x) = 2^x - \frac{x^2}{3}

We can rearrange this equation into the form of a function:

f(x)=xtan(x)2x+x23f(x) = x \tan(x) - 2^x + \frac{x^2}{3}

This function f(x)f(x) will have zeros whenever the equation xtan(x)=2xx23x \tan(x) = 2^x - \frac{x^2}{3} is true, as the zeros of f(x)f(x) correspond to the solutions of the original equation.


Step ii. Provide a plot of the graph and indicate approximate locations of three of the function’s zeros:

To plot the graph of f(x)=xtan(x)2x+x23f(x) = x \tan(x) - 2^x + \frac{x^2}{3}, we can use graphing tools like Desmos or any other graphing calculator. The plot will show the function's behavior, and we can visually estimate where it crosses the x-axis, which corresponds to the zeros of the function.

I'll describe how you can do this on Desmos:

  1. Open Desmos.
  2. In the input box, type the function: f(x)=xtan(x)2x+x23f(x) = x \cdot \tan(x) - 2^x + \frac{x^2}{3}
  3. The graph will appear, and you can zoom in/out to get a better look at the points where the graph crosses the x-axis.

Step iii. Use the Intermediate Value Theorem to show that there actually are three zeros near the ones you found by plotting:

The Intermediate Value Theorem (IVT) states that if a continuous function changes sign between two points, then there exists at least one root between them. To apply the IVT, we need to:

  • Verify that the function is continuous on the intervals we're interested in.
  • Check that the function changes sign between two points.

From the graph, we can identify three intervals where the function changes sign, indicating that there is a zero in each of these intervals. For example:

  • Let's say the graph crosses the x-axis between x1=1x_1 = -1 and x2=0x_2 = 0.
  • It also crosses between x3=1x_3 = 1 and x4=2x_4 = 2.
  • Lastly, it crosses again between x5=3x_5 = 3 and x6=4x_6 = 4.

For each of these intervals, we can apply the IVT:

  1. Continuity: The function f(x)=xtan(x)2x+x23f(x) = x \tan(x) - 2^x + \frac{x^2}{3} is continuous for all real numbers except where tan(x)\tan(x) is undefined (i.e., where x=π2+nπx = \frac{\pi}{2} + n\pi for any integer nn). We will avoid these points and focus on intervals where the function is continuous.

  2. Sign change: Let's evaluate the function at the endpoints of the intervals.

    • For x1=1x_1 = -1 and x2=0x_2 = 0, we check if f(x)f(x) changes sign.
    • Similarly, for the intervals [1,2][1, 2] and [3,4][3, 4], we check for sign changes.

For instance, if:

  • f(1)>0f(-1) > 0 and f(0)<0f(0) < 0, by the IVT, there is at least one zero in (1,0)(-1, 0).
  • Similarly, if f(1)<0f(1) < 0 and f(2)>0f(2) > 0, there is a zero in (1,2)(1, 2), and so on.

Conclusion:

By following these steps, we will verify that the function has three zeros in the intervals identified by the graph, and the IVT confirms that there are at least three solutions to the equation xtan(x)=2xx23x \tan(x) = 2^x - \frac{x^2}{3}.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Exponential Functions
Calculus
Intermediate Value Theorem

Formulas

x tan(x) = 2^x - x^2/3
Intermediate Value Theorem

Theorems

Intermediate Value Theorem

Suitable Grade Level

Grades 11-12