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13\. Exercises \(8.2 .30-32\) introduced the standard basis vectors $$\begin{array}{l}{\mathbf{i}=[1,0,0], \mathbf{j}=[0,1,0], \text { and } \mathbf{k}=[0,0,1]} \\ {\text { (a) Show that } \mathbf{i} \cdot \mathbf{j}=\mathbf{j} \cdot \mathbf{k}=\mathbf{k} \cdot \mathbf{i}=0} \\\ {\text { (b) Show that } \mathbf{i} \cdot \mathbf{i}=\mathbf{j} \cdot \mathbf{j}=\mathbf{k} \cdot \mathbf{k}=\mathbf{1.}}\end{array}$$

Short Answer

Expert verified
All dot products of different basis vectors are zero, while self-dot products are one.

Step by step solution

01

Understand the Dot Product

The dot product of two vectors \( \mathbf{a} = [a_1, a_2, a_3] \) and \( \mathbf{b} = [b_1, b_2, b_3] \) is calculated as the sum of the products of their corresponding components: \( \mathbf{a} \cdot \mathbf{b} = a_1b_1 + a_2b_2 + a_3b_3 \).
02

Calculate \( \mathbf{i} \cdot \mathbf{j} \)

Using \( \mathbf{i} = [1, 0, 0] \) and \( \mathbf{j} = [0, 1, 0] \), the dot product is calculated as \( \mathbf{i} \cdot \mathbf{j} = 1 \cdot 0 + 0 \cdot 1 + 0 \cdot 0 = 0 \).
03

Calculate \( \mathbf{j} \cdot \mathbf{k} \)

Using \( \mathbf{j} = [0, 1, 0] \) and \( \mathbf{k} = [0, 0, 1] \), the dot product is \( \mathbf{j} \cdot \mathbf{k} = 0 \cdot 0 + 1 \cdot 0 + 0 \cdot 1 = 0 \).
04

Calculate \( \mathbf{k} \cdot \mathbf{i} \)

Using \( \mathbf{k} = [0, 0, 1] \) and \( \mathbf{i} = [1, 0, 0] \), the dot product is \( \mathbf{k} \cdot \mathbf{i} = 0 \cdot 1 + 0 \cdot 0 + 1 \cdot 0 = 0 \).
05

Calculate \( \mathbf{i} \cdot \mathbf{i} \)

Using \( \mathbf{i} = [1, 0, 0] \), the dot product is \( \mathbf{i} \cdot \mathbf{i} = 1 \cdot 1 + 0 \cdot 0 + 0 \cdot 0 = 1 \).
06

Calculate \( \mathbf{j} \cdot \mathbf{j} \)

Using \( \mathbf{j} = [0, 1, 0] \), the dot product is \( \mathbf{j} \cdot \mathbf{j} = 0 \cdot 0 + 1 \cdot 1 + 0 \cdot 0 = 1 \).
07

Calculate \( \mathbf{k} \cdot \mathbf{k} \)

Using \( \mathbf{k} = [0, 0, 1] \), the dot product is \( \mathbf{k} \cdot \mathbf{k} = 0 \cdot 0 + 0 \cdot 0 + 1 \cdot 1 = 1 \).
08

Conclusion

All cross-dot products of different standard basis vectors are zero, while the dot product of each standard basis vector with itself is one.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Standard Basis Vectors
Standard basis vectors are fundamental components in vector mathematics. These vectors are unit vectors in the directions of each coordinate axis. In a 3-dimensional space, the common standard basis vectors are denoted as \( \mathbf{i} \), \( \mathbf{j} \), and \( \mathbf{k} \). To break them down:
  • \( \mathbf{i} \) is the vector \([1, 0, 0]\)
  • \( \mathbf{j} \) is the vector \([0, 1, 0]\)
  • \( \mathbf{k} \) is the vector \([0, 0, 1]\)
These vectors provide a simple and clear representation for computational purposes. They allow for easy construction of more complex vectors when we multiply them with scalars and add them together. Each vector hereby represents one axis in the system, where \( \mathbf{i} \) aligns with the x-axis, \( \mathbf{j} \) with the y-axis, and \( \mathbf{k} \) with the z-axis. They are used extensively in fields that involve physics, engineering, and computer graphics.
Vector Mathematics
Vectors are mathematical entities that have both magnitude and direction. They are used in a variety of mathematical and physical applications to represent quantities such as displacement, force, and velocity.
Vector mathematics involves operations such as addition, scalar multiplication, and the dot product. The dot product is a specific vector operation that yields a scalar result and is calculated by:
  • Multiplying corresponding components of two vectors
  • Summing the products
For instance, given two vectors \( \mathbf{a} = [a_1, a_2, a_3] \) and \( \mathbf{b} = [b_1, b_2, b_3] \), their dot product is defined as \( \mathbf{a} \cdot \mathbf{b} = a_1b_1 + a_2b_2 + a_3b_3 \).
This mathematical operation is useful for determining:
  • The angle between two vectors
  • Orthogonality, where a dot product of zero means the vectors are perpendicular
  • Projections and calculating lengths
The dot product gives insight into the directional relationship between vectors, indicating either parallel alignment or perpendicularity.
Vector Components
The components of a vector are essentially the projections of the vector along the coordinate axes. Understanding vector components is vital as they simplify complex vector operations.
Each vector in 3-dimensional space can be expressed in terms of the standard basis vectors as a linear combination of these components. For instance, any vector \( \mathbf{v} \) can be expressed as:
  • \( \mathbf{v} = v_x \mathbf{i} + v_y \mathbf{j} + v_z \mathbf{k} \)
where \( v_x \), \( v_y \), and \( v_z \) are the scalar components of the vector along the x, y, and z axes, respectively. This break-up is crucial because:
  • It simplifies calculations like the dot product and cross product.
  • It helps in visualizing the vector in space as it clearly separates effects along each axis.
By understanding and manipulating these vector components, one can effectively tackle mathematical problems in physics, engineering, and beyond. This method of breaking down vectors into components not only clarifies computation but also enhances spatial understanding of vector quantities.

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