Chapter 18: Problem 8
Draw a sketch of the given plane and find two unit vectors which are normal to the plane. $$ 4 x-4 y-2 z-9=0 $$
Short Answer
Expert verified
The unit normal vectors are \(\left(\frac{2}{3}, -\frac{2}{3}, -\frac{1}{3}\right)\) and \(\left(-\frac{2}{3}, \frac{2}{3}, \frac{1}{3}\right)\).
Step by step solution
01
Understand the Plane Equation
The given plane equation is linear and can be written as: 4x - 4y - 2z - 9 = 0. This equation is in the standard form Ax + By + Cz + D = 0 where A, B, and C are the coefficients that form the normal vector to the plane.
02
Find the Normal Vector
The normal vector \(\mathbf{N}\) to the plane is given by the coefficients of x, y, and z in the plane equation. Thus, \(\mathbf{N} = (4, -4, -2)\).
03
Calculate the Magnitude of the Normal Vector
Find the magnitude of the normal vector \(\mathbf{N}\): \[ |\mathbf{N}| = \sqrt{4^2 + (-4)^2 + (-2)^2} = \sqrt{16 + 16 + 4} = \sqrt{36} = 6 \].
04
Find the Unit Normal Vectors
Normalize the normal vector \(\mathbf{N}\) to find the unit normal vectors: \[ \mathbf{n_1} = \frac{1}{6}(4, -4, -2) = \left(\frac{4}{6}, -\frac{4}{6}, -\frac{2}{6}\right) = \left(\frac{2}{3}, -\frac{2}{3}, -\frac{1}{3}\right) \]. The other unit normal vector is the negative of \(\mathbf{n_1}\), which is: \[ \mathbf{n_2} = -\mathbf{n_1} = \left(-\frac{2}{3}, \frac{2}{3}, \frac{1}{3}\right) \].
05
Sketch the Plane
To sketch the plane, note that it intersects the coordinate axes. Set one variable to zero at a time to find intercepts: For x-intercept, set y and z to 0: \[ 4x - 9 = 0 \implies x = \frac{9}{4} = 2.25 \]. For y-intercept, set x and z to 0: \[ -4y - 9 = 0 \implies y = -2.25 \]. For z-intercept, set x and y to 0: \[ -2z - 9 = 0 \implies z = -4.5 \]. Draw a 3D coordinate system and plot these intercepts. Then, sketch the plane passing through those intercepts.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
plane equation
A plane equation in three dimensions is an essential mathematical tool, represented in the form: Ax + By + Cz + D = 0. This equation describes a flat, two-dimensional surface in a three-dimensional space. Each coefficient (A, B, and C) corresponds to the direction and orientation of the plane. In the equation 4x - 4y - 2z - 9 = 0, the coefficients 4, -4, and -2 determine the plane's slant.
Understanding this structure helps break down complex problems into more manageable parts by focusing on x, y, and z separately.
- A represents the x-component.
- B is the y-component.
- C corresponds to the z-component.
Understanding this structure helps break down complex problems into more manageable parts by focusing on x, y, and z separately.
normal vector
The normal vector is a fundamental concept in understanding planes. It is perpendicular to the plane’s surface and can be derived from the coefficients in the plane equation. Given the plane equation 4x - 4y - 2z - 9 = 0, the normal vector \(\mathbf{N}\)\ is: \[\mathbf{N} = (4, -4, -2)\]\
This vector points perpendicularly away from the plane in three-dimensional space.
The coordinates of the normal vector (4, -4, -2) indicate its direction. For visuailzation:
This vector points perpendicularly away from the plane in three-dimensional space.
The coordinates of the normal vector (4, -4, -2) indicate its direction. For visuailzation:
- 4 shows the x-direction component.
- -4 shows the y-direction component.
- -2 shows the z-direction component.
unit vector
A unit vector has a magnitude (length) of 1 and shows direction. To find a unit normal vector from our normal vector \(\mathbf{N} = (4, -4, -2)\)\, we need to normalize it. First, calculate the magnitude \(\left|\mathbf{N}\right|\)\ using: \[\left|\mathbf{N}\right| = \sqrt{4^2 + (-4)^2 + (-2)^2} = \sqrt{36} = 6\]\
With this magnitude, we can find the unit normal vectors by dividing each component of \(\mathbf{N}\)\ by 6:
\[\mathbf{n_1} = \left(\frac{2}{3}, -\frac{2}{3}, -\frac{1}{3}\right)\]\ The reverse, \(\mathbf{n_2} = -\mathbf{n_1} = \left(-\frac{2}{3}, \frac{2}{3}, \frac{1}{3}\right)\)\, is also a unit vector.
With this magnitude, we can find the unit normal vectors by dividing each component of \(\mathbf{N}\)\ by 6:
\[\mathbf{n_1} = \left(\frac{2}{3}, -\frac{2}{3}, -\frac{1}{3}\right)\]\ The reverse, \(\mathbf{n_2} = -\mathbf{n_1} = \left(-\frac{2}{3}, \frac{2}{3}, \frac{1}{3}\right)\)\, is also a unit vector.
- Step 1: Find the magnitude of \(\mathbf{N}\)\.
- Step 2: Divide each component by the magnitude.
intercepts
Intercepts are points where the plane intersects the coordinate axes. They provide reference points for sketching the plane. For the plane 4x - 4y - 2z - 9 = 0:
These intercept points (2.25, 0, 0), (0, -2.25, 0), and (0, 0, -4.5) are crucial to visualizing and sketching the plane in 3D space.
Plot these specific points on the coordinate system and draw a plane through them for a proper visualization.
- x-intercept: Set y and z to zero, \(4x - 9 = 0\)\, giving \(x = \frac{9}{4} = 2.25\)\.
- y-intercept: Set x and z to zero, \(-4y - 9 = 0\)\, giving \(y = -2.25\)\.
- z-intercept: Set x and y to zero, \(-2z - 9 = 0\)\, giving \(z = -4.5\)\.
These intercept points (2.25, 0, 0), (0, -2.25, 0), and (0, 0, -4.5) are crucial to visualizing and sketching the plane in 3D space.
Plot these specific points on the coordinate system and draw a plane through them for a proper visualization.