4- Find the volume of the solid obtained by rotating about the x-axis the region under the curve y = √5x from 0 to 4.

Calculus: Early Transcendentals
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Chapter1: Functions And Models
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### Problem Statement:

**4-** Find the volume of the solid obtained by rotating about the x-axis the region under the curve \( y = \sqrt{5x} \) from 0 to 4.

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To solve this problem, we use the method of disks (also known as the method of washers). The volume \( V \) of the solid of revolution formed by rotating a function \( y = f(x) \) around the x-axis from \( x = a \) to \( x = b \) is given by the following integral:

\[ V = \pi \int_{a}^{b} [f(x)]^2 \, dx \]

In this case, \( f(x) = \sqrt{5x} \), \( a = 0 \), and \( b = 4 \). Thus, the volume can be computed as:

\[ V = \pi \int_{0}^{4} (\sqrt{5x})^2 \, dx \]

Simplifying the integrand:

\[ V = \pi \int_{0}^{4} 5x \, dx \]

Next, we compute the integral:

\[ V = 5\pi \int_{0}^{4} x \, dx \]
\[ V = 5\pi \left[ \frac{x^2}{2} \right]_{0}^{4} \]
\[ V = 5\pi \left( \frac{4^2}{2} - \frac{0^2}{2} \right) \]
\[ V = 5\pi \left( \frac{16}{2} \right) \]
\[ V = 5\pi \times 8 \]
\[ V = 40\pi \]

Therefore, the volume of the solid obtained by rotating the region under the curve \( y = \sqrt{5x} \) from 0 to 4 about the x-axis is \( 40\pi \) cubic units.
Transcribed Image Text:--- ### Problem Statement: **4-** Find the volume of the solid obtained by rotating about the x-axis the region under the curve \( y = \sqrt{5x} \) from 0 to 4. --- To solve this problem, we use the method of disks (also known as the method of washers). The volume \( V \) of the solid of revolution formed by rotating a function \( y = f(x) \) around the x-axis from \( x = a \) to \( x = b \) is given by the following integral: \[ V = \pi \int_{a}^{b} [f(x)]^2 \, dx \] In this case, \( f(x) = \sqrt{5x} \), \( a = 0 \), and \( b = 4 \). Thus, the volume can be computed as: \[ V = \pi \int_{0}^{4} (\sqrt{5x})^2 \, dx \] Simplifying the integrand: \[ V = \pi \int_{0}^{4} 5x \, dx \] Next, we compute the integral: \[ V = 5\pi \int_{0}^{4} x \, dx \] \[ V = 5\pi \left[ \frac{x^2}{2} \right]_{0}^{4} \] \[ V = 5\pi \left( \frac{4^2}{2} - \frac{0^2}{2} \right) \] \[ V = 5\pi \left( \frac{16}{2} \right) \] \[ V = 5\pi \times 8 \] \[ V = 40\pi \] Therefore, the volume of the solid obtained by rotating the region under the curve \( y = \sqrt{5x} \) from 0 to 4 about the x-axis is \( 40\pi \) cubic units.
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