Questions: Let f(x) = 400x - 11x^2 - 9. Find the maximum value of f to four decimal places graphically.
The maximum value of f is □ .
(Round to four decimal places as needed.)
Transcript text: Let $f(x)=400 x-11 x^{2}-9$. Find the maximum value of $f$ to four decimal places graphically.
The maximum value of $f$ is $\square$ .
(Round to four decimal places as needed.)
Solution
Solution Steps
To find the maximum value of the function \( f(x) = 400x - 11x^2 - 9 \) graphically, we can follow these steps:
Plot the function \( f(x) \) over a reasonable range of \( x \) values.
Identify the vertex of the parabola, as it represents the maximum point for a downward-opening parabola.
Use Python to find and display the maximum value to four decimal places.
Step 1: Identify the Function and Its Derivative
We are given the function:
\[ f(x) = 400x - 11x^2 - 9 \]
To find the maximum value of \( f(x) \), we first need to find its critical points by taking the derivative and setting it to zero.
Step 2: Compute the Derivative
The derivative of \( f(x) \) is:
\[ f'(x) = \frac{d}{dx}(400x - 11x^2 - 9) \]
\[ f'(x) = 400 - 22x \]
Step 3: Find the Critical Points
Set the derivative equal to zero to find the critical points:
\[ 400 - 22x = 0 \]
\[ 22x = 400 \]
\[ x = \frac{400}{22} \]
\[ x \approx 18.1818 \]
Step 4: Determine the Nature of the Critical Point
To determine whether this critical point is a maximum, we can use the second derivative test. Compute the second derivative of \( f(x) \):
\[ f''(x) = \frac{d}{dx}(400 - 22x) \]
\[ f''(x) = -22 \]
Since \( f''(x) = -22 \) is negative, the function \( f(x) \) has a local maximum at \( x \approx 18.1818 \).
Step 5: Calculate the Maximum Value
Substitute \( x \approx 18.1818 \) back into the original function to find the maximum value:
\[ f(18.1818) = 400(18.1818) - 11(18.1818)^2 - 9 \]
\[ f(18.1818) \approx 400(18.1818) - 11(330.5785) - 9 \]
\[ f(18.1818) \approx 7272.7272 - 3636.3635 - 9 \]
\[ f(18.1818) \approx 3627.3637 \]
Final Answer
The maximum value of \( f \) is:
\[ \boxed{3627.3637} \]