Math Problem Statement

Write and evaluate the definite integral that represents the area of the surface generated by revolving the curve about the x-axis. y = 1 /3 x^3 from 0 to 3

Solution

The problem asks for the area of the surface generated by revolving the curve y=13x3y = \frac{1}{3}x^3 from x=0x = 0 to x=3x = 3 around the x-axis. To calculate the surface area of revolution around the x-axis, we use the formula for surface area SS of a curve y=f(x)y = f(x) rotated around the x-axis:

S=2πaby1+(dydx)2dxS = 2\pi \int_{a}^{b} y \sqrt{1 + \left( \frac{dy}{dx} \right)^2} \, dx

Step 1: Define the function and its derivative

Given y=13x3y = \frac{1}{3}x^3, let's first find the derivative of yy with respect to xx.

dydx=x2\frac{dy}{dx} = x^2

Step 2: Set up the integral

Now substitute y=13x3y = \frac{1}{3}x^3 and dydx=x2\frac{dy}{dx} = x^2 into the formula:

S=2π03(13x3)1+(x2)2dxS = 2\pi \int_{0}^{3} \left( \frac{1}{3}x^3 \right) \sqrt{1 + (x^2)^2} \, dx

This simplifies to:

S=2π0313x31+x4dxS = 2\pi \int_{0}^{3} \frac{1}{3}x^3 \sqrt{1 + x^4} \, dx

Step 3: Evaluate the integral

This integral does not have an elementary antiderivative, so we will approximate the value numerically. Let's calculate it.The surface area generated by revolving the curve y=13x3y = \frac{1}{3}x^3 from x=0x = 0 to x=3x = 3 around the x-axis is approximately 258.85258.85 square units.

Would you like further details or have any questions?

Here are 5 related questions to expand on this concept:

  1. How would the surface area change if we rotated around the y-axis instead?
  2. Can we compute the surface area for a different range, say from x=1x = 1 to x=3x = 3?
  3. What would happen to the surface area if the function were y=12x2y = \frac{1}{2}x^2?
  4. How can we find the volume generated by rotating this curve around the x-axis?
  5. How does the surface area formula differ if we rotate around a line other than the x-axis?

Tip: When setting up surface integrals, carefully handle the derivative term, as it significantly influences the final result!

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Math Problem Analysis

Mathematical Concepts

Calculus
Surface Area of Revolution
Definite Integral

Formulas

Surface area of revolution around the x-axis: S = 2π ∫ y √(1 + (dy/dx)^2) dx
Derivative of y = 1/3 x^3: dy/dx = x^2

Theorems

Surface Area of Revolution Formula

Suitable Grade Level

College-level Calculus