Chapter 14: Problem 14
Sketch position vectors for \(a, b, 2 a,-3 b\) \(a+b,\) and \(a-b\). $$ \mathbf{a}=-\mathbf{i}+2 \mathbf{j}+3 \mathbf{k}, \quad \mathbf{b}=-2 \mathbf{j}+\mathbf{k} $$
Short Answer
Expert verified
Draw vectors from origin to respective points: \((-1,2,3), (0,-2,1), (-2,4,6), (0,6,-3), (-1,0,3), (-1,4,2)\).
Step by step solution
01
Understand Position Vectors
Position vectors describe the location of a point in space relative to an origin. Here, we are given two vectors \( \mathbf{a} = -\mathbf{i} + 2\mathbf{j} + 3\mathbf{k} \) and \( \mathbf{b} = -2\mathbf{j} + \mathbf{k} \). We can represent these vectors starting at the origin and extending to the coordinate specified by each vector.
02
Sketch Vector a
Vector \( \mathbf{a} = -\mathbf{i} + 2\mathbf{j} + 3\mathbf{k} \) starts at the origin (0,0,0) and extends to (-1, 2, 3) in 3D space. Draw this vector by marking the point (-1, 2, 3) and connecting it to the origin.
03
Sketch Vector b
Vector \( \mathbf{b} = -2\mathbf{j} + \mathbf{k} \) starts at the origin (0,0,0) and goes to (0, -2, 1) in 3D space. Draw this by locating the endpoint (0, -2, 1) and connecting it to the origin.
04
Calculate and Sketch 2a
Compute \( 2 \mathbf{a} = 2(-\mathbf{i} + 2\mathbf{j} + 3\mathbf{k}) = -2\mathbf{i} + 4\mathbf{j} + 6\mathbf{k} \). This vector extends from the origin to (-2, 4, 6). Sketch this vector by extending it to the calculated point.
05
Calculate and Sketch -3b
Compute \( -3\mathbf{b} = -3(-2\mathbf{j} + \mathbf{k}) = 6\mathbf{j} - 3\mathbf{k} \). This vector extends from the origin to (0, 6, -3). Mark this point and draw the vector from the origin to there.
06
Calculate and Sketch a+b
Add vectors \( \mathbf{a} + \mathbf{b} \) to get \( (-\mathbf{i} + 2\mathbf{j} + 3\mathbf{k}) + (-2\mathbf{j} + \mathbf{k}) = -\mathbf{i} + 3\mathbf{k} \). This vector extends to (-1, 0, 3). Sketch it from the origin moving to (-1, 0, 3).
07
Calculate and Sketch a-b
Subtract vector \( \mathbf{b} \) from \( \mathbf{a} \) to get \( (-\mathbf{i} + 2\mathbf{j} + 3\mathbf{k}) - (-2\mathbf{j} + \mathbf{k}) = -\mathbf{i} + 4\mathbf{j} + 2\mathbf{k} \). It extends to (-1, 4, 2). Draw it from the origin to this point in the 3D coordinate system.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vector Addition
Vector addition involves combining two or more vectors to form a resultant vector. This is done by adding the corresponding components of the vectors together. In our exercise, we needed to find \( \mathbf{a} + \mathbf{b} \).
Visualize this in a 3D coordinate system by plotting the vector from the origin to the point \((-1, 0, 4)\).
- Start with vector \( \mathbf{a} = -\mathbf{i} + 2\mathbf{j} + 3\mathbf{k} \).
- Add vector \( \mathbf{b} = -2\mathbf{j} + \mathbf{k} \).
- The \( \mathbf{i} \) component: \( -1 + 0 = -1 \).
- The \( \mathbf{j} \) component: \( 2 + (-2) = 0 \).
- The \( \mathbf{k} \) component: \( 3 + 1 = 4 \).
Visualize this in a 3D coordinate system by plotting the vector from the origin to the point \((-1, 0, 4)\).
Vector Subtraction
Subtraction of vectors is quite similar to addition, except we're finding the difference between the vectors. We are given \( \mathbf{a} \) and \( \mathbf{b} \) and need to find \( \mathbf{a} - \mathbf{b} \).
- Vector \( \mathbf{a} = -\mathbf{i} + 2\mathbf{j} + 3\mathbf{k} \).
- Subtract \( \mathbf{b} = -2\mathbf{j} + \mathbf{k} \).
- The \( \mathbf{i} \) component: \( -1 - 0 = -1 \).
- The \( \mathbf{j} \) component: \( 2 - (-2) = 4 \).
- The \( \mathbf{k} \) component: \( 3 - 1 = 2 \).
3D Coordinate System
Understanding the 3D coordinate system is crucial for working with vectors. It consists of three axes: \( x \), \( y \), and \( z \), represented by \( \mathbf{i} \), \( \mathbf{j} \), and \( \mathbf{k} \) respectively. Each point in this system is defined by three coordinates \( (x, y, z) \). Here's how you can visualize vectors in a 3D coordinate system:
- Origin: The point where all axes intersect, typically denoted as \((0, 0, 0)\).
- Components: Each dimension contributes to defining the position of a vector.
- The vector \( \mathbf{a} = -\mathbf{i} + 2\mathbf{j} + 3\mathbf{k} \) goes from the origin to \((-1, 2, 3)\).