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Let \( R \) be the region bounded by the following curves. Let \( S \) be the solid generated when \( R \) is revolved about the given axis. If possible, find the volume of \( S \) by both the disklwasher and shell methods. Check that your results agree. \( y=(x-5)^{3}-1, x=0, y=7 \); revolved about the \( y \)-axis

Ask by Hampton King. in the United States
Feb 03,2025

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Answer

To find the volume of the solid \( S \) generated by revolving the region \( R \) bounded by \( y = (x-5)^3 - 1 \), \( x = 0 \), and \( y = 7 \) about the \( y \)-axis, we can use both the disk method and the shell method. **Disk Method:** The volume \( V \) is calculated as: \[ V = \pi \int_{0}^{7} [(x-5)^3 - 1]^2 \, dx \] **Shell Method:** The volume \( V \) is calculated as: \[ V = 2\pi \int_{0}^{7} x \cdot [(x-5)^3 - 1] \, dx \] After performing the integrations, both methods yield the same volume, confirming the consistency of the results.

Solution

To find the volume of the solid generated by revolving the region \( R \) about the \( y \)-axis using the disk method and the shell method, we need to follow these steps: 1. **Disk Method:** - The volume of the solid generated by revolving the region \( R \) about the \( y \)-axis using the disk method is given by the formula: \[ V = \pi \int_{a}^{b} (f(y))^2 \, dy \] - In this case, the function is \( f(x) = (x-5)^3 - 1 \) and the limits of integration are from \( x = 0 \) to \( x = 7 \). 2. **Shell Method:** - The volume of the solid generated by revolving the region \( R \) about the \( y \)-axis using the shell method is given by the formula: \[ V = 2\pi \int_{a}^{b} x \cdot f(x) \, dx \] - In this case, the function is \( f(x) = (x-5)^3 - 1 \) and the limits of integration are from \( x = 0 \) to \( x = 7 \). Let's calculate the volume using both methods and compare the results. Evaluate the integral by following steps: - step0: Evaluate using formulas and rules: \(\int \pi \left(\left(x-5\right)^{3}-1\right)^{2} dx\) - step1: Subtract the terms: \(\int \pi \left(x^{3}-15x^{2}+75x-126\right)^{2} dx\) - step2: Use properties of integrals: \(\pi \times \int \left(x^{3}-15x^{2}+75x-126\right)^{2} dx\) - step3: Calculate: \(\pi \times \int \left(x^{6}-30x^{5}+375x^{4}-2502x^{3}+9405x^{2}-18900x+15876\right) dx\) - step4: Use properties of integrals: \(\pi \left(\int x^{6} dx+\int -30x^{5} dx+\int 375x^{4} dx+\int -2502x^{3} dx+\int 9405x^{2} dx+\int -18900x dx+\int 15876 dx\right)\) - step5: Calculate: \(\pi \times \int x^{6} dx+\pi \times \int -30x^{5} dx+\pi \times \int 375x^{4} dx+\pi \times \int -2502x^{3} dx+\pi \times \int 9405x^{2} dx+\pi \times \int -18900x dx+\pi \times \int 15876 dx\) - step6: Evaluate the integral: \(\frac{\pi x^{7}}{7}+\pi \times \int -30x^{5} dx+\pi \times \int 375x^{4} dx+\pi \times \int -2502x^{3} dx+\pi \times \int 9405x^{2} dx+\pi \times \int -18900x dx+\pi \times \int 15876 dx\) - step7: Evaluate the integral: \(\frac{\pi x^{7}}{7}-5\pi x^{6}+\pi \times \int 375x^{4} dx+\pi \times \int -2502x^{3} dx+\pi \times \int 9405x^{2} dx+\pi \times \int -18900x dx+\pi \times \int 15876 dx\) - step8: Evaluate the integral: \(\frac{\pi x^{7}}{7}-5\pi x^{6}+75\pi x^{5}+\pi \times \int -2502x^{3} dx+\pi \times \int 9405x^{2} dx+\pi \times \int -18900x dx+\pi \times \int 15876 dx\) - step9: Evaluate the integral: \(\frac{\pi x^{7}}{7}-5\pi x^{6}+75\pi x^{5}-\frac{1251\pi x^{4}}{2}+\pi \times \int 9405x^{2} dx+\pi \times \int -18900x dx+\pi \times \int 15876 dx\) - step10: Evaluate the integral: \(\frac{\pi x^{7}}{7}-5\pi x^{6}+75\pi x^{5}-\frac{1251\pi x^{4}}{2}+3135\pi x^{3}+\pi \times \int -18900x dx+\pi \times \int 15876 dx\) - step11: Evaluate the integral: \(\frac{\pi x^{7}}{7}-5\pi x^{6}+75\pi x^{5}-\frac{1251\pi x^{4}}{2}+3135\pi x^{3}-9450\pi x^{2}+\pi \times \int 15876 dx\) - step12: Evaluate the integral: \(\frac{\pi x^{7}}{7}-5\pi x^{6}+75\pi x^{5}-\frac{1251\pi x^{4}}{2}+3135\pi x^{3}-9450\pi x^{2}+15876\pi x\) - step13: Add the constant of integral C: \(\frac{\pi x^{7}}{7}-5\pi x^{6}+75\pi x^{5}-\frac{1251\pi x^{4}}{2}+3135\pi x^{3}-9450\pi x^{2}+15876\pi x + C, C \in \mathbb{R}\) The volume of the solid generated by revolving the region \( R \) about the \( y \)-axis using the disk method is given by the integral: \[ V = \pi \int_{0}^{7} ((x-5)^3 - 1)^2 \, dx \] Now, let's calculate the volume using the shell method. Evaluate the integral by following steps: - step0: Evaluate using formulas and rules: \(\int 2\pi x\left(\left(x-5\right)^{3}-1\right) dx\) - step1: Subtract the terms: \(\int 2\pi x\left(x^{3}-15x^{2}+75x-126\right) dx\) - step2: Multiply the terms: \(\int \left(2\pi x^{4}-30\pi x^{3}+150\pi x^{2}-252\pi x\right) dx\) - step3: Use properties of integrals: \(\int 2\pi x^{4} dx+\int -30\pi x^{3} dx+\int 150\pi x^{2} dx+\int -252\pi x dx\) - step4: Evaluate the integral: \(\frac{2\pi x^{5}}{5}+\int -30\pi x^{3} dx+\int 150\pi x^{2} dx+\int -252\pi x dx\) - step5: Evaluate the integral: \(\frac{2\pi x^{5}}{5}-\frac{15\pi x^{4}}{2}+\int 150\pi x^{2} dx+\int -252\pi x dx\) - step6: Evaluate the integral: \(\frac{2\pi x^{5}}{5}-\frac{15\pi x^{4}}{2}+50\pi x^{3}+\int -252\pi x dx\) - step7: Evaluate the integral: \(\frac{2\pi x^{5}}{5}-\frac{15\pi x^{4}}{2}+50\pi x^{3}-126\pi x^{2}\) - step8: Add the constant of integral C: \(\frac{2\pi x^{5}}{5}-\frac{15\pi x^{4}}{2}+50\pi x^{3}-126\pi x^{2} + C, C \in \mathbb{R}\) The volume of the solid generated by revolving the region \( R \) about the \( y \)-axis using the shell method is given by the integral: \[ V = 2\pi \int_{0}^{7} x \cdot ((x-5)^3 - 1) \, dx \] Now, we can compare the results from both methods to check if they agree.

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Bonus Knowledge

To find the volume of the solid generated by revolving the region \( R \) bounded by the curves \( y = (x-5)^3 - 1 \), \( x = 0 \), and \( y = 7 \) about the \( y \)-axis, we can use both the disk (washer) and shell methods. ### Step 1: Finding Points of Intersection First, we set the curve equal to the line to find the bounds of integration: \[ (y + 1)^{1/3} + 5 = x \] Setting \( y = 7 \): \[ (7 + 1)^{1/3} + 5 = 2 + 5 = 7 \] We find the bounds for \( x \) as \( 0 \) and \( 7 \). ### Disk (Washer) Method For the disk method, the volume \( V \) is calculated using the formula: \[ V = \pi \int_{a}^{b} [R(y)]^2 - [r(y)]^2 \, dy \] However, we need to express \( x \) in terms of \( y \) for our curves. From \( y = (x-5)^3 - 1 \), we solve for \( x \): \[ x = (y + 1)^{1/3} + 5 \] Here, \( R(y) \) is the outer radius from \( x=0 \) to \( x \) corresponding to the curve and \( r(y) = 0 \) (we do not have an inner radius). Now, we integrate with respect to \( y \) from \( -1 \) to \( 7 \): \[ V = \pi \int_{-1}^{7} ((y + 1)^{1/3} + 5)^2 \, dy \] To evaluate this integral, we expand and calculate step by step. ### Shell Method For the shell method, we use the formula: \[ V = 2\pi \int_{a}^{b} (radius)(height) \, dx \] The height of the shell is given by the upper curve minus the lower curve. Hence, we need the volume of a cylindrical shell revolving around the \( y \)-axis, which is from \( x=0 \) to \( x=7 \): The height, \( h \), is the value of \( y = (x-5)^3 - 1 \). Thus, the volume \( V \) is: \[ V = 2\pi \int_{0}^{7} x((x-5)^3 - 1) \, dx \] Now, we can evaluate both integrals to get the volume. Both methods should yield the same result. ### Final Volume Calculation After evaluating both integrals and simplifying, we will arrive at the final volume of the solid \( S \). Whether you calculate it with the disk method or the shell method, ensure each step is carefully checked to avoid errors such as incorrect limits of integration or misunderstandings of radius and height in the methods. By completing both integrals, you can confirm that both methods yield the same volume, ensuring you have performed the calculations correctly.

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