Math Problem Statement

Find the volume V of the solid obtained by rotating the region bounded by the curves y = x^3 and y = 5x about the line x = 3.

Solution

The image contains a calculus problem that reads:

"Find the volume V of the solid obtained by rotating the region bounded by the curves y = x^3 and y = 5x about the line x = 3."

Solution:

To find the volume VV of the solid formed by rotating the region bounded by y=x3y = x^3 and y=5xy = 5x about the line x=3x = 3, we can use the method of cylindrical shells.

Step 1: Set up the integral for the volume using the cylindrical shells method.

The volume VV using the cylindrical shells method is given by:

V=2πab(rshell)(hshell)dxV = 2\pi \int_{a}^{b} (r_{\text{shell}})(h_{\text{shell}}) \, dx

Where:

  • rshell=distance from the axis of rotation=3xr_{\text{shell}} = \text{distance from the axis of rotation} = 3 - x
  • hshell=height of the shell=5xx3h_{\text{shell}} = \text{height of the shell} = 5x - x^3 (difference between the functions)

Step 2: Determine the bounds of integration.

We need to find the intersection points of the curves y=x3y = x^3 and y=5xy = 5x:

x3=5xx^3 = 5x

x(x25)=0x(x^2 - 5) = 0

This gives:

x=0orx=5orx=5x = 0 \quad \text{or} \quad x = \sqrt{5} \quad \text{or} \quad x = -\sqrt{5}

However, since we're dealing with the region bounded by x=0x = 0 and x=5x = \sqrt{5}, we will integrate from 0 to 5\sqrt{5}.

Step 3: Set up the integral.

V=2π05(3x)(5xx3)dxV = 2\pi \int_{0}^{\sqrt{5}} (3 - x)(5x - x^3) \, dx

Step 4: Expand and integrate.

Expanding the integrand:

(3x)(5xx3)=15x3x35x2+x4(3 - x)(5x - x^3) = 15x - 3x^3 - 5x^2 + x^4

The integral becomes:

[ V = 2\

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Math Problem Analysis

Mathematical Concepts

Calculus
Volume of Solids
Cylindrical Shells Method
Integration

Formulas

Volume using Cylindrical Shells: V = 2π ∫(r_shell * h_shell) dx
Intersection of curves: x^3 = 5x

Theorems

Cylindrical Shells Method

Suitable Grade Level

Grades 11-12 or Early College