Math Problem Statement

Use the shell method to find the volume of the solid generated by revolving the region bounded by y equals 11 x minus 10​, y equals StartRoot x EndRoot​, and x equals 0 about the​ y-axis.

Solution

To find the volume of the solid generated by revolving the region bounded by y=11x10y = 11x - 10, y=xy = \sqrt{x}, and x=0x = 0 about the y-axis using the shell method, we will follow these steps:

Step 1: Understanding the shell method

The formula for the volume of a solid generated by revolving a region about the y-axis using the shell method is:

V=2πab(radius of shell)×(height of shell)dxV = 2\pi \int_{a}^{b} \text{(radius of shell)} \times \text{(height of shell)} \, dx

  • The radius of the shell is the distance from the y-axis, which is just xx.
  • The height of the shell is the difference between the upper curve y=11x10y = 11x - 10 and the lower curve y=xy = \sqrt{x} at a particular value of xx.

Step 2: Determine the bounds of integration

To determine the bounds of integration, we need to find the points of intersection of y=11x10y = 11x - 10 and y=xy = \sqrt{x}.

Set 11x10=x11x - 10 = \sqrt{x}:

11x10=x11x - 10 = \sqrt{x}

Squaring both sides to eliminate the square root:

(11x10)2=x(11x - 10)^2 = x

Expanding the left-hand side:

121x2220x+100=x121x^2 - 220x + 100 = x

Simplifying:

121x2221x+100=0121x^2 - 221x + 100 = 0

Now, we solve this quadratic equation using the quadratic formula:

x=(221)±(221)24(121)(100)2(121)x = \frac{-(-221) \pm \sqrt{(-221)^2 - 4(121)(100)}}{2(121)} x=221±4884148400242x = \frac{221 \pm \sqrt{48841 - 48400}}{242} x=221±441242x = \frac{221 \pm \sqrt{441}}{242} x=221±21242x = \frac{221 \pm 21}{242}

Thus, the two solutions are:

x=221+21242=242242=1x = \frac{221 + 21}{242} = \frac{242}{242} = 1 x=22121242=200242=100121x = \frac{221 - 21}{242} = \frac{200}{242} = \frac{100}{121}

Therefore, the points of intersection are at x=1x = 1 and x=100121x = \frac{100}{121}. These will be the bounds for the integration.

Step 3: Set up the integral for the volume

The radius of a shell is xx, and the height of the shell is the difference between the two curves, (11x10)x(11x - 10) - \sqrt{x}.

The volume integral is:

V=2π1001211x((11x10)x)dxV = 2\pi \int_{\frac{100}{121}}^{1} x \left( (11x - 10) - \sqrt{x} \right) dx

Step 4: Simplify and compute the integral

We now expand the integrand:

V=2π1001211(x(11x10)xx)dxV = 2\pi \int_{\frac{100}{121}}^{1} \left( x(11x - 10) - x\sqrt{x} \right) dx V=2π1001211(11x210xx3/2)dxV = 2\pi \int_{\frac{100}{121}}^{1} \left( 11x^2 - 10x - x^{3/2} \right) dx

Now, integrate each term separately:

11x2dx=11x33\int 11x^2 \, dx = \frac{11x^3}{3} 10xdx=5x2\int -10x \, dx = -5x^2 x3/2dx=2x5/25\int -x^{3/2} \, dx = -\frac{2x^{5/2}}{5}

Thus, the volume is:

V=2π[11x335x22x5/25]1001211V = 2\pi \left[ \frac{11x^3}{3} - 5x^2 - \frac{2x^{5/2}}{5} \right]_{\frac{100}{121}}^{1}

Step 5: Evaluate the integral

Substitute the bounds x=1x = 1 and x=100121x = \frac{100}{121} into the expression for the volume.

At x=1x = 1: 11(1)335(1)22(1)5/25=113525\frac{11(1)^3}{3} - 5(1)^2 - \frac{2(1)^{5/2}}{5} = \frac{11}{3} - 5 - \frac{2}{5}

At x=100121x = \frac{100}{121}, plug in x=100121x = \frac{100}{121} and simplify.

Finally, subtract the two values and multiply by 2π2\pi.


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Math Problem Analysis

Mathematical Concepts

Calculus
Volume of solids
Shell method
Integration

Formulas

V = 2π ∫ (radius of shell) × (height of shell) dx
Quadratic formula: x = (-b ± √(b² - 4ac)) / 2a

Theorems

Shell method for volume of revolution
Quadratic equation solution

Suitable Grade Level

Grades 11-12