Chapter 3: Problem 3
The equation of a right eircular cylinder, whose axis in the \(z\)-axis and radius \(a\) is \((a) x^{2}+y^{2}+z^{2}=a^{2}\) (b) \(a^{2}+y^{2}=a^{2}\) (c) \(x^{2}+y^{2}=a^{2}\) \(\left(\right.\) d) \(2^{2}+x^{2}=a^{2}\)
Short Answer
Expert verified
The correct equation is (c) \(x^2+y^2=a^2\).
Step by step solution
01
Understanding the geometry of a cylinder
A right circular cylinder whose axis is along the \(z\)-axis means that the shapes formed by slicing the cylinder perpendicular to the \(z\)-axis are circles. The cylinder can be described by the equation for a circle in the \(xy\)-plane.
02
Identify the equation for a circle
The equation for a circle with center at the origin \((0, 0)\) in the \(xy\)-plane is \(x^2 + y^2 = r^2\), where \(r\) is the radius of the circle. In this case, the radius is given as \(a\).
03
Determine the equation of the cylinder
For a cylinder that extends along the \(z\)-axis, the circular cross-section remains constant across all values of \(z\). Therefore, the equation of the cylinder, unaffected by \(z\), is \(x^2 + y^2 = a^2\).
04
Select the correct option
Upon examining each given choice:(a) \(x^2 + y^2 + z^2 = a^2\) describes a sphere.(b) \(a^2 + y^2 = a^2\) simplifies to \(y = 0\), not a cylinder.(c) \(x^2 + y^2 = a^2\) matches the determined equation.(d) \(2^2 + x^2 = a^2\) doesn't match the required form.Thus, the correct answer is (c) \(x^2+y^2=a^2\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
right circular cylinder
A right circular cylinder is a three-dimensional shape that features two parallel circular bases and a curved surface connecting them. These bases are of equal radius and aligned directly opposite one another. It is called 'right' because the sides make a right angle with the bases.
This shape is common and extensively used in both geometry and real-life applications, such as cans and pipes.
This shape is common and extensively used in both geometry and real-life applications, such as cans and pipes.
- The radius of the cylinder, typically denoted by "a" or "r", is the distance from the center to the edge of the base.
- The height or the length of the cylinder is the perpendicular distance between the two bases.
geometry of a cylinder
The geometry of a cylinder can be broken down into several key properties. These include its height, radius, and surface area, which describe the basic elements.
- Surface area: Consists of both the lateral surface area plus the area of the two bases. The lateral surface area is evaluated by "unrolling" the curved surface into a rectangle.
- Volume: Calculated by multiplying the base area by the cylinder height. This captures the capacity of the cylinder.
- Cross-sections: For a cylinder aligned along a particular axis, its perpendicular cross-sections will always be circular, maintaining the original radius.
cylinder axis along z-axis
When a cylinder's axis is along the z-axis, its symmetry is developed around this vertical line. This scenario is often used in mathematics due to its alignment with coordinate planes.
With the axis on the z-axis, the problem simplifies to one of planar geometry in the xy-plane.
With the axis on the z-axis, the problem simplifies to one of planar geometry in the xy-plane.
- This means any cross-section along a constant z will result in a circle.
- The equation you derive reflects this simplicity: it is independent of the z-coordinate, shown as: \(x^2 + y^2 = a^2\).
equation of a sphere
The equation of a sphere is often confused with that of a cylinder, due to their reliance on similar square terms. Specifically, a sphere has the form
\(x^2 + y^2 + z^2 = r^2\), where \(r\) is the radius of the sphere.
This equation denotes that all points on the sphere are equidistant from the center, making it a purely radial symmetry.
\(x^2 + y^2 + z^2 = r^2\), where \(r\) is the radius of the sphere.
This equation denotes that all points on the sphere are equidistant from the center, making it a purely radial symmetry.
- In contrast to cylinders, spheres use all three coordinate directions in \(x\), \(y\), and \(z\).
- This distinguishes the sphere from a cylinder, which maintains its shape primarily in two directions and remains unaffected by changes in the third direction.