Chapter 9: Problem 17
A plane has normal vector \(n\) and passes through the point \(P\). (a) Find an equation for the plane. (b) Find the intercepts and sketch a graph of the plane. $$\mathbf{n}=\left\langle 3,0,-\frac{1}{2}\right\rangle, \quad P(2,4,8)$$
Short Answer
Expert verified
(a) Plane: \( 3x - \frac{1}{2}z = 2 \); (b) Intercepts: x = \( \frac{2}{3} \), y undefined, z = -4.
Step by step solution
01
Understand the Plane Equation
The general equation for a plane in 3D space can be written as \( ax + by + cz = d \), where \( \mathbf{n} = \langle a, b, c \rangle \) is the normal vector to the plane.
02
Substitute the Normal Vector
Given the normal vector \( \mathbf{n} = \langle 3, 0, -\frac{1}{2} \rangle \), substitute \( a = 3 \), \( b = 0 \), and \( c = -\frac{1}{2} \) into the plane equation, so we have \( 3x + 0y - \frac{1}{2}z = d \) which simplifies to \( 3x - \frac{1}{2}z = d \).
03
Use the Given Point to Find d
Substitute the coordinates of point \( P(2, 4, 8) \) into the equation \( 3x - \frac{1}{2}z = d \) to find \( d \). Using \( x = 2 \), \( y = 4 \), and \( z = 8 \), we substitute to get \( 3(2) + 0(4) - \frac{1}{2}(8) = d \), which simplifies to \( 6 - 4 = d \), thus \( d = 2 \).
04
Write the Plane Equation
Now substitute \( d = 2 \) back into the equation \( 3x - \frac{1}{2}z = d \), yielding the plane equation: \( 3x - \frac{1}{2}z = 2 \).
05
Find the Intercepts
To find the x-intercept, set \( y = 0 \) and \( z = 0 \). Equation becomes \( 3x = 2 \), hence \( x = \frac{2}{3} \). For the y-intercept, set \( x = 0 \) and \( z = 0 \). Since \( b = 0 \), the y-intercept is not defined in this equation. For the z-intercept, set \( x = 0 \) and \( y = 0 \), resulting in \( -\frac{1}{2}z = 2 \), so \( z = -4 \).
06
Sketch the Plane
Sketch the plane using the x-intercept (\( \frac{2}{3}, 0, 0 \)) and the z-intercept (\( 0, 0, -4 \)). The line through these points will lie in the plane alongside other potential points if needed. The plane is parallel to the y-axis due to \( b = 0 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Normal Vector
The normal vector is a fundamental concept in 3D geometry, particularly when we're dealing with planes. A normal vector to a plane is one that is perpendicular to the plane itself. This is what makes it "normal" or orthogonal. For the given problem, the normal vector is \( \mathbf{n} = \langle 3, 0, -\frac{1}{2} \rangle \).
- Orientation: The normal vector gives us the orientation of the plane. In this problem, \( a = 3 \), \( b = 0 \), and \( c = -\frac{1}{2} \) determine how the plane is tilted in 3D space.
- Equation Contribution: These components correspond directly to the coefficients in the plane equation \( ax + by + cz = d \), which fundamentally defines the plane.
Intercepts
Intercepts are points where a plane or line crosses the axes in the coordinate system. For any plane equation, identifying intercepts is key because they provide tangible points to understand and sketch the plane.
- x-intercept: In our problem, setting \( y = 0 \) and \( z = 0 \) results in \( 3x = 2 \). Solving for \( x \), we find \( x = \frac{2}{3} \). So, the x-intercept is \( \left( \frac{2}{3}, 0, 0 \right) \).
- y-intercept: Normally, you find the y-intercept by setting both \( x = 0 \) and \( z = 0 \). However, in our case, since \( b = 0 \), the y-term is missing, indicating the plane never actually crosses the y-axis in the usual manner.
- z-intercept: Setting \( x = 0 \) and \( y = 0 \), we find \( -\frac{1}{2}z = 2 \), leading to \( z = -4 \). Thus, the z-intercept is \( (0, 0, -4) \).
3D Geometry
3D geometry involves the study of mathematical shapes in a three-dimensional space, where concepts such as planes, lines, and points interact. A plane in 3D geometry is a flat, two-dimensional surface that extends infinitely along its length and width but has zero thickness.
- Plane Representation: The equation of a plane is typically given in the form \( ax + by + cz = d \). In simpler terms, this represents all the points (x, y, z) that lie on the plane.
- Planes in Space: Because a plane is two-dimensional, it divides the 3D space into two halves. The position of the plane is uniquely determined by a normal vector and a point lying on the plane, allowing it to exist in specific orientations within the space.
- Graphical Representation: Sketching a plane can be aided using its intercepts which act as reference points. By connecting intercept points, like the ones found in the exercise, we can simulate the infinite plane in a finite 2D sketch.