Chapter 4: Problem 39
For the following exercises, plot a graph of the function. $$z=f(x, y)=\sqrt{x^{2}+y^{2}}$$
Short Answer
Expert verified
The graph is a three-dimensional conical surface centered at the origin.
Step by step solution
01
Understand the Function
The function given is \( z = f(x, y) = \sqrt{x^2 + y^2} \). This function is the formula for the distance from the origin to a point \((x, y)\) in the xy-plane. It represents a three-dimensional surface known as a conical surface, also called a cone with a circular cross-section.
02
Identify the Shape of the Function
The function \( z = \sqrt{x^2 + y^2} \) describes a conical surface where the value of \( z \) depends on the distance of the point \((x, y)\) from the origin. As \( x \) and \( y \) increase in magnitude from zero, \( z \) also increases, forming a circular cone that opens upward from the origin.
03
Choose Graphing Range
To plot the graph of the function, choose appropriate values for \( x \) and \( y \). Common ranges include \( x \) from -5 to 5 and \( y \) from -5 to 5 to adequately show the shape of the cone and its symmetry around the origin.
04
Plot Corresponding Points
Calculate \( z \) for selected pairs of \( x \) and \( y \) within the chosen range. For example, calculate \( z \) for \((x, y)\) pairs like (0,0), (3,4), (-4,3), etc. This will give points \((x, y, z)\) that lie on the surface of the cone.
05
Draw the Graph
Using the calculated points, plot \( z = \sqrt{x^2 + y^2} \) on a three-dimensional graph. The graph will form a cone with its vertex at the origin (0,0,0) and a circular base as it extends outward. Lines of equal distance \( z \) from the origin will form circles parallel to the xy-plane.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Conical Surface
A conical surface is a 3D geometric shape that looks like a cone. The function given, \( z = \sqrt{x^2 + y^2} \), describes such a surface where the height \( z \) above any point \((x, y)\) is determined by its distance from the origin. This equates to a circle in the xy-plane that extends upwards to form a cone.
- Vertex: The cone's tip is at the origin \((0, 0, 0)\).
- Axis: The axis of the cone runs along the z-axis.
- Circular Cross-section: Any cross-section parallel to the xy-plane will be a circle.
3D Graphing
Graphing in three-dimensional space involves plotting values for three variables, typically \( x, y, \) and \( z \). The function \( z = \sqrt{x^2 + y^2} \) provides a perfect opportunity to explore 3D graphing.
- Coordinate System: Use a Cartesian coordinate system with axes for \( x, y, \) and \( z \).
- Graphing Range: Choose a range, e.g., \( x \) and \( y \) from -5 to 5, which provides a complete view of the shape.
- Plot Points: For each pair of \( (x, y) \), calculate \( z \), giving points \((x, y, z)\) on the surface.
Distance Formula
The distance formula is a key mathematical tool and its 2D version is useful in our function. The expression \( \sqrt{x^2 + y^2} \) is the distance from the origin to the point \((x, y)\) in the xy-plane.
- Origin: It references the fixed starting point \((0, 0)\) in 2D.
- Purpose: Calculates how far a point is from the origin, effectively mapping the radius of our conical cross sections.
- 3D Extension: In 3D, the general distance formula becomes more complex, but here provides heights for our function.
Coordinate Systems
Coordinate systems are essential for mapping mathematical functions into a space that we can visualize. In this context, our function uses a Cartesian coordinate system, which is perfect for describing surfaces like cones.
- Axes: Consists of three perpendicular axes - \( x, y, \) and \( z \).
- Representation: Places points in a space relative to these axes where each axis reflects a dimension.
- 3D Function Placement: Here, each point has coordinates \( (x, y, z) \), allowing for precise positioning of the surface.