Chapter 11: Problem 35
Sketch the surfaces in Exercises \(13-44\) $$y=-\left(x^{2}+z^{2}\right)$$
Short Answer
Expert verified
The surface is a downward-opening paraboloid centered at the origin.
Step by step solution
01
Identify the Shape of the Surface
The given equation is \(y = -(x^2 + z^2)\). Recognize that this equation represents a paraboloid that opens downwards along the y-axis, since \(y\) is negating the terms \(x^2 + z^2\), both squared terms.
02
Analyze Cuts in Coordinate Planes
To better understand the surface's structure, let's analyze cross-sections:- **Plane \(x = k\):** The equation becomes \(y = -(k^2 + z^2)\), which is a parabola in the \(yz\)-plane.- **Plane \(z = k\):** The equation is \(y = -(x^2 + k^2)\), another parabola in the \(xy\)-plane.Both will intersect on a parabola opening downward along the negative y-axis.
03
Sketch the Surface
To sketch the surface:1. Draw the y-axis going negative, as the maximum value of y is 0, occurring when \(x = 0\) and \(z = 0\).2. Draw parabolas that open downward, centered at the origin on both the \(yz\) and \(xy\)-planes at several slices. These parabolas should show the surface folding downwards uniformly along all directions defined by x and z.
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Coordinate Planes
Coordinate planes are essential in visualizing and analyzing three-dimensional surfaces and objects. The three main coordinate planes in a three-dimensional Cartesian coordinate system are the xy-plane, yz-plane, and xz-plane.
- The xy-plane is where the z-coordinate is zero, and it extends infinitely in the x and y directions.
- The yz-plane is defined by x = 0, extending infinitely in the y and z directions.
- The xz-plane is the plane where y = 0, and it extends infinitely along the x and z axes.
Cross-sections
Cross-sections are a powerful tool to understand the three-dimensional shapes by taking two-dimensional slices of them. Imagine taking a knife and cutting through a loaf of bread to see the pattern inside; this is similar to analyzing cross-sections.
For the paraboloid described by the equation \( y = -(x^2 + z^2) \):
For the paraboloid described by the equation \( y = -(x^2 + z^2) \):
- In the plane x = k, the equation becomes \( y = -(k^2 + z^2) \). This results in a parabolic cross-section in the yz-plane. The parabola opens downward along the y-axis, maximizing at the origin.
- Similarly, in the plane z = k, the equation is \( y = -(x^2 + k^2) \), which gives another parabolic cross-section in the xy-plane, also opening downward.
Surface Sketching
Surface sketching is a method of visual representation to better understand and interpret the shape and features of mathematical surfaces. Sketching begins by plotting key features like vertices, axes, and notable cross-sections, and combining them into a coherent image.
When sketching the paraboloid described by \( y = -(x^2 + z^2) \), several steps are useful:
When sketching the paraboloid described by \( y = -(x^2 + z^2) \), several steps are useful:
- Begin by drawing the y-axis, prominently showing the negative direction since y decreases indefinitely.
- Mark the key point of the surface, which is the origin (0,0,0), where \( y \) reaches its highest value, 0.
- Use vertical slices to draw parabolas on both the yz and xy-planes. Each parabola appearing as a downward "U", shows the shape curving downwards from the origin.
- Connecting these parabolas smoothly helps visualize the complete surface creating a dome-like appearance, emphasizing the downward opening nature.