Question:medium

The volume of the region bounded by the cylinders \( x^2 + y^2 = 4 \) and \( x^2 + z^2 = 4 \) is _________ (rounded to TWO decimal places).

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To compute the volume of the intersection of two cylinders, use cylindrical coordinates and set up an appropriate triple integral based on the geometric constraints.
Updated On: Feb 2, 2026
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Solution and Explanation

Step 1: Geometric interpretation (Steinmetz solid).
The region is the intersection of two perpendicular cylinders:

• \(x^2+y^2 \le 4\) (cylinder along the \(z\)-axis)
• \(x^2+z^2 \le 4\) (cylinder along the \(y\)-axis)

Their intersection is a classical Steinmetz solid.


Step 2: Use slicing with respect to \(x\).
Fix a value of \(x\). From the first cylinder: \[ y^2 \le 4-x^2 \] From the second cylinder: \[ z^2 \le 4-x^2 \]

For a fixed \(x\), the cross-section in the \(yz\)-plane is a square:

\[ - \sqrt{4-x^2} \le y \le \sqrt{4-x^2}, \quad - \sqrt{4-x^2} \le z \le \sqrt{4-x^2} \]

Side length of the square: \[ 2\sqrt{4-x^2} \]

Area of the cross-section: \[ A(x)=\left(2\sqrt{4-x^2}\right)^2=4(4-x^2) \]


Step 3: Set up the volume integral.
The bounds for \(x\) are determined by: \[ x^2 \le 4 \;\Rightarrow\; -2 \le x \le 2 \]

Hence, \[ V=\int_{-2}^{2} 4(4-x^2)\,dx \]


Step 4: Evaluate the integral.

\[ V=4\int_{-2}^{2}(4-x^2)\,dx \]

\[ =4\left[4x-\frac{x^3}{3}\right]_{-2}^{2} \]

\[ =4\left[\left(8-\frac{8}{3}\right)-\left(-8+\frac{8}{3}\right)\right] \]

\[ =4\left(\frac{32}{3}\right)=\frac{128}{3} \]


Final Answer:

\[ \boxed{\dfrac{128}{3}\;\approx\;42.67} \]

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