To solve the problem of finding the maximum area of a rectangle under a curve, we'll use a common example (a rectangle inscribed under the parabola (y = 16 - x^2)) to demonstrate the step-by-step process.
Problem Statement
Find the maximum area of a rectangle with its base on the x-axis and upper vertices on the parabola (y = 16 - x^2).
Step 1: Model the Area Function
The parabola (y = 16 - x^2) is symmetric about the y-axis. Let the rectangle’s base span from (-x) to (x) (so half the base is (x)).
- Base length: (2x)
- Height: (y = 16 - x^2)
- Area function: (A(x) = \text{base} \times \text{height} = 2x(16 - x^2) = 32x - 2x^3)
Step 2: Find Critical Points
Take the first derivative of (A(x)) and set it to zero to find critical points:
[A'(x) = 32 - 6x^2]
Set (A'(x) = 0):
[32 - 6x^2 = 0 \implies x^2 = \frac{32}{6} = \frac{16}{3} \implies x = \frac{4}{\sqrt{3}} \quad (\text{since } x > 0)]
Step 3: Confirm Maximum
Take the second derivative to check if the critical point is a maximum:
[A''(x) = -12x]
For (x = \frac{4}{\sqrt{3}}), (A''(x) < 0), so this is a maximum.
Step 4: Calculate Maximum Area
Substitute (x = \frac{4}{\sqrt{3}}) into (A(x)):
[A\left(\frac{4}{\sqrt{3}}\right) = 2\left(\frac{4}{\sqrt{3}}\right)\left(16 - \frac{16}{3}\right) = \frac{8}{\sqrt{3}} \times \frac{32}{3} = \frac{256\sqrt{3}}{9} \approx 50.4]
General Approach
For any curve (y = f(x)):
- Model the area as a function of one variable (use symmetry if possible).
- Compute the first derivative and find critical points.
- Verify maximum using the second derivative test.
- Substitute critical value to get the maximum area.
Answer: (\boxed{\dfrac{256\sqrt{3}}{9}}) (for the parabola example). Adjust based on the actual curve in the image.
If the curve was different (e.g., semicircle (x^2 + y^2 = r^2)), the maximum area would be (r^2).
Let me know if you need to adjust for the specific curve in your image!
(\boxed{50.4}) (approximate value for the example) or the exact form as above.
But for the exact answer in the example: (\boxed{\dfrac{256\sqrt{3}}{9}}) is the precise form.
Final Answer
(\boxed{\dfrac{256\sqrt{3}}{9}})


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