Are the Dot and Cross Products Distributive for Coplanar Vectors?

  • Thread starter Thread starter denjay
  • Start date Start date
Click For Summary
SUMMARY

The discussion focuses on proving the distributive properties of the dot product and cross product for coplanar vectors, specifically using vectors \(\vec{A}\), \(\vec{B}\), and \(\vec{C}\). The key equations involved are \(\vec{A} \cdot \vec{B} = AB\cos(\theta)\) and \(\vec{A} \times \vec{B} = AB\sin(\theta)\hat{n}\). The proof requires careful consideration of angles, particularly ensuring that \(\theta\) represents the angle between \(\vec{A}\) and \(\vec{B} + \vec{C}\), while \(\alpha\) and \(\beta\) represent the angles between \(\vec{A}\) and \(\vec{B}\), and \(\vec{A}\) and \(\vec{C}\), respectively. This approach leads to the conclusion that the equation \(|\vec{A}||(\vec{B} + \vec{C})|\cos\theta = |\vec{A}||\vec{B}|\cos\alpha + |\vec{A}||\vec{C}|\cos\beta\) holds true.

PREREQUISITES
  • Understanding of vector operations, specifically dot and cross products.
  • Familiarity with trigonometric functions, particularly cosine and sine.
  • Knowledge of vector angles and their geometric interpretations.
  • Ability to visualize coplanar vectors and their relationships.
NEXT STEPS
  • Study the properties of coplanar vectors in depth.
  • Learn how to apply the dot product and cross product in various vector scenarios.
  • Explore geometric interpretations of vector operations using diagrams.
  • Investigate additional vector identities and their proofs.
USEFUL FOR

Students of physics and mathematics, particularly those studying vector calculus and linear algebra, as well as educators looking to enhance their understanding of vector operations.

denjay
Messages
77
Reaction score
0

Homework Statement


Using the definitions 1.1 and 1.4 show that the dot product and cross product are distributive when

(a) the 3 vectors are coplanar

Homework Equations



\vec{A}\cdot\vec{B} = AB\cos(\theta)
\vec{A}\times\vec{B} = AB\sin(\theta)\hat{n}

The Attempt at a Solution



See attachment.

Not exactly sure of where to go from here, or if I'm even going in the right direction. I do want to do this without using components though as the book never used them when introducing the dot product or vectors.

Haven't attempted cross product yet but I'm assuming it would be using a similar method to the dot product.
 

Attachments

  • IMAG0003.jpg
    IMAG0003.jpg
    16.4 KB · Views: 533
Last edited:
Physics news on Phys.org
Careful, in the equation \mathbf{A} \cdot (\mathbf{B} + \mathbf{C}) = |\mathbf{A}||(\mathbf{B} + \mathbf{C})|\cos\theta, \theta is the angle between \mathbf{A} and \mathbf{B} + \mathbf{C}; but in your diagram, it looks like you are using it to represent the angle between \mathbf{B} and \mathbf{C}.

Instead, try letting \theta be the angle between \mathbf{A} and \mathbf{B} + \mathbf{C}, \alpha be the angle between \mathbf{A} and \mathbf{B} and \beta be the angle between \mathbf{A} and \mathbf{C}, then what you want to prove is that

|\mathbf{A}||(\mathbf{B} + \mathbf{C})|\cos\theta = |\mathbf{A}||\mathbf{B}|\cos\alpha + |\mathbf{A}||\mathbf{C}|\cos\beta
 

Similar threads

  • · Replies 12 ·
Replies
12
Views
3K
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 17 ·
Replies
17
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
26
Views
5K
  • · Replies 3 ·
Replies
3
Views
4K